Stressed stepmom- Thanks for sharing your experience. I may be being impatient, then, as ds has only lived w/us since August. And the relationship between your son & DH sounds a lot like the relationship between mine. DH sees himself more as a buddy...it makes sense that it would take some time. Ds's move with us coincided w/my last trimester & then birth of our daughter almost 3 weeks ago, so everyone's plate is full.
As far as your experience w/DH's ex rewarding the kids for being defiant, I didn't have that experience, luckily. That has to suck. You, however, have the benefit of much experience with children, and your husband's daughters sound like they are probably old enough to handle an honest discussion with you, where you let them know you are aware that they're being encouraged not to listen to you, and ask them how they feel about it and what effect it may have on individuals and the family as a whole.
And some totally unasked-for advice: I'd ask their mom to meet and talk, and if she won't do that, write her a letter and let her know that you absolutely respect that she is their mom, and that you don't want to interfere with their relationship w/her, and ask if there's anything you can do to help her/them feel more comfortable about the situation. Maybe short & sweet on a card would do it. But she's acting that way because she feels insecure, and it can't hurt to be the 'bigger person' and offer some security.
I had an interesting dynamic w/my son's stepmom- she wanted to be called "Mom" and badmouthed me. I gritted my teeth and supported her 100% to my ds as I didn't want him to be conflicted. I took him to buy Mother's Day cards and Xmas gifts for her. I asked her to meet so we could talk and she never would. I wrote her a letter and later email, and she never responded. The only times we talked were specifically about ds.
Before ds moved back w/me in August she met w/ex & me to discuss the move and stated emphatically that she believed ds should stay w/them and that if his dad and I both died, she'd want to raise ds as she loved him like her own son (which I believed as she's been his stepmom since he was 2). HOWEVER, after ds moved w/me, she & ex revealed that their marriage was falling apart, they separated and she, who supposedly loved him like her own, only called ds once for his bday (after I left a vm on her cell reminding her). Ds is feeling pretty abandoned. I don't know if I should contact her or not, let her know that she's welcome to continue her relationship with ds- again- or just let it go.