Does she want to leave or divorce him? If so maybe you could help her set up a temporary arrangement so that she won't be afraid to not leave for financial reasons. The kids may be the hardest part though. Depending on how old they are perhaps they should be made aware of what's going on so if any sudden changes happen they can be taken care of. Usually the religious advice in spousal conflicts is to seek counsel but from your description of the events his conduct demonstrates he's ignoring the religious guidelines. So assuming she does want a divorce she should first separate and get the kids in a position where she doesn't have to worry about them being taken away.

If she fears outcast by the community I don't think she should let that deter her. Either they're not aware of the details of the situation or they're simplisitic/ignorant and view and a woman divorcing a manipulative and controlling husband as bad. If during the separation the two reconcile their differences, seek counseling and eventually decide not to divorce I guess that's their right but it doesn't seem like it would happen in this case especially if he's going around accusing her of sleeping with your husband since accusations of adultery are pretty slanderous. Obviously that seems unlikely since seems more like this guy enjoys controlling her and I usually don't see that change in the context of relationships. Perhaps you could try speaking with the imam (religious leader) or someone else at their local mosque so that they can intercede with the community perception/backlash part of this if needed.