Like yours, my DH didn't have my back for many years, his two kids disrespected me and he never said anything to them. Finally, when they were in their 20s, we moved away and shortly after that, his elder daughter went to war with me and started insulting me etc to him, and to me by email.  Initially he threatened me with divorce if I didn't appease her.  I refused to do so and told him to do his worst. He has now been in therapy for 2 yrs and things are improving between us - he has better boundaries with them and, more importantly, I stand up for myself in a way I never did, before.  

I advise you to do the same, ie stand up for yourself, don't allow anyone to disrespect you, including your DH. Unless he finally gets some perspective on his co-dependent relationship with his teen kids, I would not think you have a viable relationship with him.  Like you, I have two older kids who both have children of their own. I was prepared to end this marriage if he didn't change.  

If he doesn't make your marriage a priority, how can he expect you to? It doesn't work if it's only a priority to one partner.

Saying, "See how if feels?" seems childish but it's hard to imagine that he's not getting it, that it's exactly what he's doing to you by putting his kids first all of the time. You shouldn't have to spell it out for him, especially since it's already been addressed by the marriage counselor.

Some people just don't have the capicity to balance a relationship when they already have kids (and should stay single). 

Maybe one day (hopefully, soon), he will have an epiphany but until then, keep doing what you are doing and live your life. 

How long have you been disengaged from the kids?  From DH?

It took a while for my DH to get it and it wasn't just me disengaging silently. It was more like, me saying, "No, I'm not going to pick up OSD from her bus stop because I'll have to wait an hour for her in town. I wasn't asked if her plans were ok or included int the decision making so you can go get her yourself." Or, "I will not make dinner any longer when the SDs are here. Their food issues have become to difficult to deal with and my trying to help is not improving it and it takes me too long to cook - you will have to be the primary cook when they are here but I'll do it now and then if I feel like it and let you know."

Boundary, rational explanation, calmly stated, follow through.

Edit - I did actually silently disengage from arranging fun things. If DH wanted to do something, I'd tell him to go ahead and plan it or if I saw something fun I just woudn't say anything because DH could very well keep an eye out for things too.

As others have said, a marriage with only one partner who is all in is not sustainable.

I lived that for myself. I was all in on my first marriage. My XW was not in at all.

I let it go on for far too long.  There was only token intimacy. In the 27mos from wedding until she moved out, there were two 8mos periods with zero intimacy.  Not on the wedding night, not on the 10day honemoon except for once on the last day.  Not for the next 8mos after the honeymood.  In the 27mos we were married, we were fully intimate only 7 times.   She on the otherhand, was exceptionally active from an intimacy perspective.  Just not within the marriage.  Any intimacy within the marriage was driven entirely by me with initiation every single night.  If she was not going to be intimate, I made sure she had to actively reject me every single night.

A different situation that what your STBXH is perpetrating against you intimacy wise. But, basically the same outcome. No effort towards marital intimacy.  Even my cheat of an XW engaged in at least token level intimacy. Though under constant pressure.

If your DH is not making an effort  regarding intimacy, that is on him. I tried with my XW, she not only tried but actively participated with any swinging Johnson she could climb, outside of the marriage.

Fortunately the marriage only lasted 30mos wedding to final divorce hearing.  More fortunately, I did not pollute my gene pool with her.

Even with all of her games, toxicity, etc... I was not yet at my end point. Fortunately she played the D card.  As soon as she did, I motivated the rapid end. Though I would not have initiated pulling the plug for likely far too long had she not informed me that she wanted a divorce.  In hind sight, she had little choice since she was knocked up by her geriatric Fortune 500 executive sugar/baby daddy. when she walked out of the final marriage therapy session after 7mos.  We had done a lot of work on communication, her relationship with her family, my relationship with my family, etc... At the openning of the last joint session the Doc informed us that it was time to start working on addressing the lack of intimacy in the marriage.  XW stood up, prouned she did not have a problem with sex, and walked out.  She never returned. She moved out 8wks later a week after informing me she wanted a divorce.  I learned not long after that that she had been cheating throughout the engagement, and the marriage.

Her serial adultery gave me a reprieve, set me on rediscovering the man I enjoy being, gave me the beginning of my new life adventure and on the path of living my best life.  Which is also the best revenge.  I have lived that revenge with gusto for nearly 34 years.  DW and I have seen and lived in much of the world, and love the life we are making together.

XW is at last count on DH #3 (I was #1), has three all out of wedlock spawn by two different men. Her eldest and youngest are cheat babies conceived with fuck buddies while married to someone not the father.  Grandpa Sugar/Baby daddy married her after their second child was born. He divorced her when she got knocked up with her 3rd child. That one fathered by a cheat buddy while she was stepping out on the guy she stepped out with while married to me.  I have to say, I quite enjoyed the karma bus they were both run over by with XW's whoring.

So, enjoy your new life and live it with gusto.

Take care of  you.

Get out, save yourself.  

Good luck.

All IMHO and experience of course.

This is just my opinion but the marriage is not equal to those kids - it comes before those kids (unless they're in imminent danger, have terminal illness, etc)

Those kids will be fine and in fact they need (yes it is a need) to see y'all in harmony because you all are leading they way and setting the example of what happy healthy marriage should look like as a standard for their own marriages when they reach that stage. 

In fact when kids are grown and out of the house, it's just y'all two, you are at risk of having nothing with each other just being strangers or roommates if marriage isn't just a prioritized if not more than daily childrearing. 

You could even use reverse psychology on him stating if kid needs come first then he is disrespecting his kids by not putting you alls marriage as a priority bc kids need that stability in the home. 
 

Also if he is making efforts to change (when you said he asks you to events with him and you say no) then you may want to be open and receptive if you can because once resentment sinks in it's very difficult to repair the relationship. 
 

spend time together especially on weekends his kids aren't there.

You get to be the main, cook, cleaning lady.  For his kids?  Is this a way to live.?  If you can't compromised on dinner tine, meal choice . Then cook for yourself, eat when you want.  Let DH and or the SK, Shoped fotbygevfoid, cooked it. Eat it and clean up.  No reason to fight over it.    If you can't have an emotional ..sexual  relationship with DH. It's tine for a exit plan.  DH needs to see someone,

you can't go on in life with no emotional relationship with your man.  You will be looking for someone else .  What's not fair.  to anybody.  Better to leave and start looking for someone else, out in the open.  You only have a few years on earth. You only go around once.  You better not throw those years away being unhappy 

These are such incredibly difficult situations. Had my DH not fully participated in counseling with me and had he not stood his ground with the ingrates and lunatic ex, we would not be married.  For some reason, people seem to listen more to that third party (a sibling, a friend, a therapist), and people kept telling him that his kids were going to move on in life--without him--so why would he put his marriage at risk by catering to their impossible demands? Is there anyone else your husband will listen to that will wake him up?! 

I couldn't live my life with my feelings getting hurt all the time and my values and needs being trampled on--NO ONE should. So, I get your disengagement. 

You are doing what is called the 180.  It comes from the book Divorce Busting.  DH has a choice to make, them or the marriage.  Keep on taking care of yourself, but do leave him chances to join you.  Being with you should be more pleasant and fun than anything else.   If he comes along and picks a fight and just generally ruins the time together then counseling and a visit to lawyer (or a few) to gather facts for yourself would be in order.    

What is very hard to do. Is not caring about then at all.  It's hard because your money or family money is going towards them living.   But we know this when we started.  But truly not caring if they live, how they live , how they function.  As if they eat, have clothes to wear. Where they go, if they come home.  Disengagement also means not caring about any future GK  coming along. 
'You will NOT be the defacto babysitter.  If SO wants to babysit that's of course up to him 

I have had many many moments where I was ready to leave the marriage. I still would be willing to leave, but I too love my home.

Especially since in this area I would not be able to afford things on my own. We got in super cheap, and super low rates in the refi.

But you need to visit a lawyer, see what your options actually are.