My guess is she will want them back in a hurry rather than cut daddy a check every month.

At 17, these young women are in all liklihood a lost cause.  Only they will be able to resolve their issues. If they find the motivation to do so.  Likely, exept for the public humiliation that will invariably find them, they won't recognize that they behave as pigs.

Don't waste your time and emotional health on them.

Good luck

I'm inclined to reluctantly agree with Rags that they're probably too old to change.  But how do they react to you?  If they seem to want to be like you, or gain your admiration, you might be able to have an influence.  Does your DH see their behavior issues?  Thankfully, they dont sound like some of the possessed witches we hear about on Steptalk, just immature and awkward.

A couple of phrases come to mind here.

"You can't care more than the biological parents"

and 

"connection without Correction breeds resentment"

How did these girls get to be like this at 17 without both of their parents doing more to prepare them for the world?

Why doesn't your SO want to help his kids improve.. and do the work himself.. teaching them.. encouraging them.. getting them therapy if necessary etc?  It's not your place or your job to do any of that.

If you try to step in with new rules.. expectations.. they will just resent you and likely cry to mommy and daddy.. stirring up drama in  your life.. you will be villainized.  Don't fall into this trap.

You seem like a nice, well meaning woman.. but the bottom line is your SO is who needs to be doing this.

...on top of everything else. Their shyness and introversion may be the result of them relying on each other rather than being encouraged to socialize with others, especially if their own mother was hands-off and didn't do much for them.

Perhaps your husband can look into getting them both to enlist in the military when they turn 18?  It will certainly teach them self-discipline and encourage independence. 

I would also point out that there is a difference between not wanting to grow up.. being anxious about adult responsibilities.. and not having been taught to be more "adult"

They sound atrocious.  Are they going to Ireland with you or staying behind?   Are you married?  You have a vote in how you expect to live your life.  This could be your hill to die on.  What is dad's plan to get them out on their own? Does he even have one?  Does he have an urgency about it or is carefree about them, expecting YOU to complete HIS responsibilities for them?  This will take over your whole marriage and life if you let it and he probably will, no guy is worth that IMO.   

You are also trying to pin this on the "mother who clearly did nothing".. but your DH absolutely proactively enabled these girls by doing everything for them.. that's just as guilty as mom in how they turned out.  (also.. take these stories about exes with a grain of salt.. you are hearing his side.. which may or may not be the same as full on reality.. though clearly his girls aren't allstars)

Take   BM,,CS and what you we're paying in CS. Abd hire a cleaning person .  To clean up after the SD and other household ckeanibg ti help you out 

These girls are 17 years old. Not only did their mother fail them, so did their father. I love what ESMOD said. You will be seen as an enemy on any instruction you try to direct at these ALMOST adults. YOU will have zero impact. This work is for YOUR DH. Not you. Regardless of your intentions (which are good), he's the only one  that can do anything with his kids. 

With the little you've shared on his behaviors (cleaning up their mess before mom got home), I'd say you have a DH problem. If he's not willing to address his own kids' serious life issues, those girls will be with you for YEARS if not forever. Research this site for stories of other SMs who have to deal with failures to launch along with coping techniques. If you stay with this man, you will need to start preparing for life in StepHell. 

I agree with the other posters.  This is not your problem and at age 17, I also feel like it's a lost cause.  It sounds like their mother did nothing, but it seems to me that their dad had an obligation to address their behavior and teach them things too.... it sounds like both parents failed them.  Another concern I would have is whether or not these two girls every launch as adults.  CajunMom's post pretty much sums that up - you may be dealing with these two girls well into the future, if not forever. 

I don't think you should try to help them - you will be met with resentment and you will become the "evil stepmother."  DH needs to work with them and if he is unwilling, well, you need to think long and hard about the situation and what you want for your future. 

As other posters have mentioned, you can't care more than the parents.  Disengage and put this issue in DH's lap.

Please keep us posted - and take care of yourself......

There is some mental health problems here.  At 17 you would think they would learn from TV. Friends classmates.

There some not firing on all cylinders here.  You would think they know of "Boys". And you want to smell good for them. Not embarrassing themselves in front of classmates 

As the mother of twin daughters, this smacks of neglect. It seems that they have been pretty much left to their own devices seeing as they had someone to play with so the parents didn't bother. Father cleaned up after them? Got them jobs? All for the sake of appearances ... not for his daughters' good. Nobody taught them to socialize with others and as they had each other, nobody really worried about them. They have gone beyond the "normal" twin bond and would appear to be co-dependent. OP, can you do things with them separately or do they resist? I'm betting that they resist. Nobody has ever taught them to use cutlery? I've only ever seen that once and it was in a teen whose mother never had time for him (the kid was going home for lunch and having to fend for himself with whatever he found in the fridge ... at age 7).

Were they dressed the same as children? Put in the same classes? Never had any extracurriculars? Never had any sleepovers? Friends? Just a few questions to think about.

Why doesn't their father care enough about them to help them develop, become independent? You can't put it all on their mother, he's a parent too.

I'm not sure there's much you can do for them at this late date. Talk to them as if they were standard teens of their age. Ask them (separately) to do things with you (one goes with you and the other with her father). Above all, get their father involved. If he protests that he IS involved, ask him why he's never had them evaluated or gotten them the help they needed. 

And its about kids who refuse to listen.

he basically said there is an age, about 6-7 that you have before kids are set in their ways and its almost impossible to reverse the damage already done.

as parents, our job when we choose to have kids, is to raise and nurture them to be productive members of society and for others to have to tolerate them without them being total a-holes.

problem is so many parents sadly fail in this basic role then wash their hands off the problem they created and contributed to yet expect the general public to tolerate their crap. 
 

there are some who will say they refuse to leave skids behind, that its horrible of us to say "you can't care more than the bio parents or do the job they fail and refuse to do"

it doesn't matter if bio parent works away, they needto ensure whilst they are away that they follow through with basic behaviours, household rules and basic expectations. Palming this off to stepparent is so they can be the baddy and you the fun parent 

fun parents who raise kids with no discipline, basic expectations and manners etc, tend to raise entitled kids who expect the world given to them for nothing 

First off, how long has your husband been divorced from their mother? Has it been a long time or has it been a short time? If these girls have been with him a lot, it's obviously because their mother doesn't care and he's trying to be Mr. nice guy. Now that you're married to him, you need to sit down and make a set of rules. You need to both back up the rules. Start with chores. Use a check board.  I'm sure he does in the military. 
 

if their mother does not like them, I'm sure it is weighing on their minds. My ex-husband made the "no rules" in the family while I was the strict one - so it seemed easy for my own biological daughter. She lived with him for a under 2 years until she realized that was really stupid. She immediately came back to my DH and me. She also respected her SF. ...More than her BF .There is a time when there's a realization that the world has rules and you kind of have to follow them. Hopefully your DH will realize that his BK s Are not going to walk all over you and hopefully he will get with the program. At 17 though? This will not be easy. It can be done because my stepdaughter and biological daughter were teenagers when we did it.

(My BD has got twins. And her DH has teenagers, and they have it all set up with rules. As his son is basically out of the house now in college however, all of the kids follow the rules/they took the best of hers in the best of his. If his teenagers could adapt to her rules which are really different than their mothers? It can be done.)

Do they have what used to be called Charm school near your new home? That could certainly help with the manners without you being the bad guy. It might help them gain confidence and learn to interact in the world.

Charm school or an etiquette class. If there isn't one nearby,  hold one at home! Just talk to DH and the girls about their age and tell them you'd like to help them learn "grown up" manners. Since they seem immature,  this might not be offensive to them, but if it is just gently explain that approaching 18 is time to polish some skills. Teach them to set the table and at mealtime show them how to hold silverware and use a knife to cut food and placing the napkin in the lap and to chew quietly. This is one you can practice at home regularly and reinforce it. If they aren't receptive,  you tried. 

It does sound like there is a psychological component here that very likely effects their behavior,  but you may be able to get some modifications in to at least be able to have a meal in a restaurant without incident.  

It sounds like you're a very kind person with the best of intentions,  so I applaud your wanting to help them.  Just know that step land is full of landmines for most of us, but once in a while you hear of great relationships coming from step parents and skids, so it does happen for some. 

Enlist support from DH to help back you up on everything, though. That makes all the difference in the world!