I would suggest that you work with your girls to be more respectful to their dad. It probably feels good inside to know he's hearing the OW called a whore to his face; that's got to be really uncomfortable for him and he deserves it.
But your daughters are practicing being what kind of adults they're going to be now, and you need to be their role model. They can say what they feel, and should, but in a way that is respectful and without insults. He has hurt them badly, he is hardly ever seeing them, and they are mad. He should absolutely hear that. They dislike the idea of OW and the fact of OW, plus everything else about her, and have every right to say so. But they should try to do it calmly and without inflammatory language.
They want to punish H, but that is not really for them to do. Better for them to work with what they get to build the best type of relationship with him that they can. Boy does it suk and it is not fair, but there it is. It is better for them in the longrun to have a relationship with their dad even if he's being a crummy one.
I'm sorting all this out in preparation for handling the exact same cr*p with my own 14 and 12yo and I don't like it either. But you gotta do what is best for them.
You mentioned that you don't control what they do and say to him, and you shouldn't, but you should talk with them about your values and respectful language and grace under pressure.
They should know that they have ZERO control over what happens with your marriage. They probably think, or subconsciously anyway, that if they hate him or are mean and nasty about OW that will either bring him back, or make him rethink what he's doing, or at least get what's coming to him. But the result is going to be more damage to them. It's not their responsibility to defend you or punish H or anything but grow up healthy and strong, and hopefully able to weather the storm with you.
Adinva 51, S20, S18 M24 total 6/15/11-12/1/12 From IDLY to H moving out 9/15/15-3/7/17 From negotiating SA to final D at age 50 5/8/17-now: New relationship with an old friend __ Happiness is a warm puppy.