Date: May 10, 2017 02:16PM
I'll add my two cents that there is hope that your husband may be able to connect with his children, but it's likely to still be a bumpy road.
My wife was in a similar situation as your husbands daughter. Her Mother has a significant but un-diagnosed illness (Borderline Personality Disorder). Her parents were married for a while, even though things were bad, very bad, they had two kids (including my wife). Her mother eventually cheated on her Dad and the two divorced.
It took a long time, like a very long time, but eventually my wife realized that her parents relationship wasn't a healthy one when they were married (in many ways it's still not, even though they are divorced, have both remarried, they still have contact through family functions and lets just say that we avoid having family functions that require both sides to be together when possible).
Anyway, my wife was finally able to talk to her Dad and get his side of the story, which to me, was much more reasonable and rational sounding. He was just a guy who did his best with a wife he simply couldn't understand and was never going to understand. He loves his kids, even now, he'll bend over backwards to help us, he's a great guy and it took a long time for my wife to unravel the lies, poison and anger that her mother used to taint the father-daughter relationship. But she did, and she's glad that she was able to do that.
If I were to advise anything for you and your husband (take it as you will, your situation could be very different hand ours.), it would be to stay out of any conversation regarding "the mother". Answer specific questions, if asked, but do so as factually as possible, keeping emotion out of it. I know how hard that can be, if it helps, keep things focused on his daughter and her family. And watch your boundaries. Living with a mentally ill person can be damaging to a person's ability to know what proper boundaries should be, make sure you know what you're comfortable with and what you're not comfortable with going into this. Also watch for strong emotional statements and for strong escalations in emotion. I mean like, things are going a long just fine and you or your husband says something you feel is harmless and carries no negative statement at all, only for the daughter to have a strong angry reaction because she took the statement completely different than you expected. (Her emotional example, her mother, probably hasn't been the best)
I also recommend reading a book titled "Stop Walking on Eggshells: Taking Your Life Back When Someone You Care About Has Borderline Personality Disorder" even though his ex may or may not have BPD, and his daughter might not either, learning how to communicate and deal with people who have strong emotional reactions to things can be invaluable rebuilding relationships like this. The reason I bring this up is because it wasn't that long ago that this daughter thought it was OK to slap her father for drinking a beer, that reaction is out of proportion, even if the daughter objects to a beer. It may take her a long time out from under the direct influence of her mother to break some of those mental habits. Knowing how to watch for signs of emotional dis-regulations and how to deal with them can help save you and your husband and even his daughter some pain.
Anyway, I hope this is a good first step for your husband and his daughter (and really you too, you're in there as well). Today, my wife and her father enjoy a happy relationship, far better than my wife and her mother. They go out to lunch, we have him and his wife over frequently for dinners, etc. The relationship can be repaired, give it time, but do be prepared for the bumps in the road.