It sounds like the husband wants to just continue biting his tongue to maintain access to the children, but LW is uncomfortable not standing up for her son and what she believes is right. It might be better for her, psychologically, and maybe even for the rest of them, to confront the issue head on, but then again, it might drive their daughter further away; and even if her husband isn't physically or emotionally an abuser, the sect they've joined is a cult-type and inherently abusive authoritarian culture. As I understand it, the advice for loved ones lost to cults and the like is the same as for ones in abusive relationships - to simply remain available. Not that that precludes telling their daughter where they stand, I guess.

But perhaps then she needs to have a serious debate with her husband about their future course since a confrontation could cut them both off from the children...