You've already discussed with your husband the fact he didn't respond in real time after he admits to hearing it. 
You do you now. No need tonwaste anymore time discussing with PowerSulk- she'll come out the victim. 
You and husband might discuss your plans but it's up to him whether he communicates with his offspring. Be done done with her. 

I wouldn't waste one more minute of energy on Powersulk. No meetings, no discussions, not fake apologies.

Live your best life and keep your boundaries high and mighty. Your husband will undoubtedly need repeated reminders about this, and that's the only energy I'd spend.

I'm going to give my frank opinion then answer your question.

You have been in an emotionally abusive family dynamic for so long that you don't recognize it's still emotionally abusive (or at least toxic) because it's better than it has been. But better doesn't mean it's good or healthy. You haven't actually accomplished anything with your husband or his kids. The only thing that has changed is the kids got older and disengaged from the two of you. Your husband replaced Toxic Troll with Barnacle Buddy. You still want to placate everyone without having to make big changes to your life.

I don't say any of this in malice. As an outsider looking in, what I see is you say you have boundaries, but they are holding back the toxicity as well as a chain-link fence holds back a flood. You are a good-hearted person that WANTS to put good in the world, but those in your immediate vicinity are emotional vampires who are sucking up all your goodwill. And you just keep trying to find ways that you can keep pouring it all out.

Your SD crossed a boundary with you. You're never getting an apology. You're never going to actually convince her that what she did was wrong. Her own father let it go. Her mother helped teach her this behavior. You are in a super losing battle here with exactly no one on your team except you.

So prune your family tree. SD is now cut off - emotionally, physically, financially. You won't be in the house with her while she is there. She shows up, you leave. She asks for something, you direct her immediately to her father. You don't talk about her, you don't ask about her, and you shut down any conversations about her. You don't keep explaining why you're doing it. They all know why; they're just hoping to squeeze a little bit more out of you to fulfil their own selfish desires.

Also, even though you're husband isn't actively saying or doing toxic crap to you doesn't mean he is suddenly a good husband. He had every opportunity to stand up for you and he didn't. He tried to weasel SD into what could be a date night for you both. Ask yourself - why are you the ONLY person in his life that he is willing to be a d*ck to? Is it because you're the only one who won't push back? He sucks. Massively. And he should be sad and depressed about it because he hasn't done one mother-effing thing to improve anything.

The best way to disengage is to just do it, not announce it.  You just become TOTALLY unavailable for anything and anyone  that treats you in a toxic way.  You love yourself more. By doing that you don't put yourself in situations and conversation that go nowhere.  
 

DH is now telling you what you want to hear is the hopes he can get you to calm down and assume your place that he wants you in.  Let that sink in and then let the anger burn inside you do it motivates you to action.  

meditate on those words because they are full truth. I do not want to come across as mean spirited or negative but LtDad said it perfectly....you've gained zero ground. I'd also tread lightly with DHs "awakening" as I have heard the same damn things from my DH with his kids. (We are currently in yet another battle concerning behaviors of his 30 and 40 year old daughters and I'm hearing a lot of the same stuff).

No need to announce the disegagement. You've told your DH, now begin. And don't look back. As humans, we can demand an apology but we cannot force someone to do it. And really, what value is a forced apology? I've had a bunch of those...totally useless. Same with the family meetings...you will get the "smoke blown up your ass" treatment and within a few weeks, every thing goes back to "normal". Ask me how I know.

And now you know why I've continued my complete cutoff from DHs kids. They're POS humans and their father, my DH, still thinks they are "sweet widdle babies" that cannot take the truth of their shit behaviors, regardless of who points it out. And yes, we are back in counseling because of him standing by and letting his nutter 30 year old daughter taunt and antagonize me on my own property. No worries...I handled it...told that biotch to get off my property immediately. I tell you this, not to take away from your current issue but to let you know I'm in a very similar battle....not as devestating emotionally as yours, but similar in DH actions.

CLove, I'm in your corner, sweet Lady. Cut that girl out of your life. Let the crazy mother and her father handle any and all issues for this person and you take care of YOU. Hugs.

Instead of discussing anything, plant your flag, make your declaration, and immediately put it on them to test your resolve at their peril.

To DH: "I am through sacrificing my peace of mind and quality of life to your failed parenting. Either you get yourself and your spawn under control and keep them in their place, or I will and none of you will like it."

To SDPS/etc: "If you ever are disrespectful to me again, you are out of my home and my life. This is a zero chance stipulation. Do not make the mistake of pulling any of the shit you usually pull, or your idiot mother and nasty sister pull. If  you do, including one rolled eye, one sulky sigh, etc.. you will never again cross the door of my home or receive the benefit of once Cent of benefit from my efforts. You are on the final steps of your walk of doom to adulthood. In 40wks you nor your idiot mother will get a Cent from this marriage. Your are cut off from CS on your birthday. If you want event a remote chance of getting any benefit from or belonging to this family, knock your shit off now."

Or something along these lines.

Then, show them, show yourself.  No more talking. Just taking action to apply consequences to them, and living your best life. Defend that life.

IMHO of course.

I love the power words, and the Power-CLove. 

Do you think ageing out going to, do anything.  Put your foot down.   SD is not allowed in your home,  no ifs and buts.  DH wants to see hid DD. He can do it at the park.  If SD cones to your home, that the lasts time you do anything for DH.  Cook, clean. Ect.  Disengage total from SD 

Do you think ageing out going to, do anything.  Put your foot down.   SD is not allowed in your home,  no ifs and buts.  DH wants to see hid DD. He can do it at the park.  If SD cones to your home, that the lasts time you do anything for DH.  Cook, clean. Ect.  Disengage total from SD 

I would start cleaning out SD room tomorrow, her bed gone, her clothes gone, her stuff gone. Let her call CPS. You seriously think CPS is going to waste there time with a 17 yo .  Then change the locks on the doors 

You said

"1. an apology. (?)

2. a famly discussion with all of us. And what do we say?

3. I make it known that there will no longer be outtings together, and why. And Repeat this.

4. I start planning what Im going to do when she ages out of visitation - to include plans for using the room as storage and guest room/snoring room. And make it known to both of them. Immediately. If not now, when should this talk come up?"

Do none of these. The time for explaining, convincing and announcing what you're going to do are over.

You quietly focus on yourself.

If either one of them makes demands on you. Calmly say, "I'm not comfortable with that" or "Ask your dad" or "that's not going to work for me."

No apologies. No explanations. No announcements. If you want to be gone or busy when she visits - do so. If you prefer to be home, just stay busy with your stuff and do not ask SD about ANYTHING. She makes a mess? Leave it. She wants to bend your ear? "I think you should talk to your dad."

He tries to manipulate you or make you feel bad about not doing things for him or SD or he tries to start an argument? Stay calm and just say, "No thanks" or "I've got other plans" or "I'm not comfortable with that".

You don't need their approval or buy in or to know that you're done. They know you're done. Stop announcing it. Just prove that you're really done by disengaging - completely.

I thought you had a long game plan to leave?  If so why are you considering the possibility of her moving in ??  Which is it?  I don't think you have committed one way or another in your mind or heart, so you come across as wishy washy in your posts of late.  One day your ready to pitch it all in the fire , the next you post about some "breakthrough " someone had.   Do a deep dive in lot all of your previous posts and take a hard look at all the toxic crap they have put you through, done to you.  

I probably would have called her mother or grandparents or whoever to come get her. 
 

then I would have called the husbands work wife and told her come get him too! 
 

im kidding. 
 

But seriously your husband was out of order hearing his spawns verbally abuse you and do nothing. Just as abusive to allow you to be abused .... in your own home. 
 

That's a one way ticket to marital celibacy. I'd take sex off the table until he came correct!

There's no need for apologies because they wiould be insincere and fake.  No need for a family discussion because it won't change anything long-term.  No need for great declarations of what will and won't happen because PS and DH have learned it won't take long for you to crack and things will go back to the status quo they prefer.  

The time for talk is over unless it's to discuss the division of assets between you and DH, and you've made it clear you're not ready for that.  PS doesn't need to darken your doorstep.  Find a cheap efficiency apartment and tell DH that's where he gets to have his visitation with her from now on.  He can deal with her BS all on his lonesome.  It doesn't matter if neither of them like it - they've earned a place for just the two of them.  You shouldn't have to leave your house because she wants to come over.  DH has made it clear he's not going to protect you from PS, and he'll do whatever he can to prevent you from protecting yourself so as not to upset her.

I honestly hope you get to the point you just don't GAF anymore. Don't care what they do, where they do it, as long as they aren't around you.  It's been my experience in relationships that's when the other person (or people) realized they couldn't walk all over me anymore.  They simply didn't matter.

1. Apology. Why bother? It'll be insincere and meaningless.

2. Family meeting. Why bother? Powersulk isn't your family - that's been made pretty clear.  She's just your H's kid who uses you when it suits her purposes. 

3. Outings. You already said there won't be any.  There's no need to reiterate it. Just make sure there aren't any.  Probably the one you need to tell this to over and over is yourself. 

4. The age out.  The only one who possibly needs to hear about your plans for when Powersulk ages out is your H. Let him know your boundary. If that's no adult children living with you, full or part time, tell him that.  There is absolutely no need to announce it to Powersulk. And no need to tell your husband if it's not a boundary you intend to hold.  You tend to draw lines in the sand and then back up when your H and his baggage jump over the line. I'd quietly formulate a plan of what you'll do if your boundaries regarding PS once she turns 18 and graduates are not respected, and get yourself in a position to be able to effect that plan.

Lieutenant Dad is spot on - there haven't really been any changes here. The only one you can change is yourself. Your H and his toxic and dysfunctional family aren't going to change.