WTBH, really big ((((hugs))))
I am really sorry you are going through this. As for the SR responses, well when you ask a bunch of codies for advice you might as well be offering vodka to an A. It's what we do. Again I really don't have anything I can share that I think would help your situation.
I have one big question for you though. If you let him see the girls at either your mother's house or yours , without your supervision, do you think he would be a danger to them? If not I would use this as an opportunity to work on my detachment and let him see them. Doing so would take away a big argument he has about you trying to control his access to them.
Dam, see what just happened, you asked a codie for advice, I was just going to give support and the next thing you know my mouth is running away giving solutions to problems that I don't own. Doesn't mean the advice might not be worthwhile though.
If nothing else you have my support and any strength that I can send.
Your codie friend,