I tell you, I do feel for your situation. You can not just sit idle with the hope nothing really happens but you also can not be Superman to everyone in need also. We went through this years ago with my wife's sister. Amazes me that my wife and her sister were actually raised together, 2 completly different outlooks on life.
Anyways, I offered her sister to come live with us for a while, we lived about an hour and half away. One of the conditions was no contact with him, at all. He had threatened my wife in terms of she better not get involved "or else" kind of line and I told him I will bury him without a thought, he apologized to my wife and never spoke to her again. Ended up she never came to stay with us but my wife did alert child services. Nothing came of it and thankfully he ended up doing about 8 months in prison for drug possession/dealing. In that time she grew strong enough that it was officially over, she finally wasn't going to go back to how it was. I really think they have to decide that on their own and by you offering to help her if she gets to that point is about all you can do.
Anyways, I offered her sister to come live with us for a while, we lived about an hour and half away. One of the conditions was no contact with him, at all. He had threatened my wife in terms of she better not get involved "or else" kind of line and I told him I will bury him without a thought, he apologized to my wife and never spoke to her again. Ended up she never came to stay with us but my wife did alert child services. Nothing came of it and thankfully he ended up doing about 8 months in prison for drug possession/dealing. In that time she grew strong enough that it was officially over, she finally wasn't going to go back to how it was. I really think they have to decide that on their own and by you offering to help her if she gets to that point is about all you can do.