Trust your gut!
Your gut is telling you to stay away from his mother. Trust your gut.
I'm sorry that your feelings are being minimized. This is your home too. You have rights.
I agree with Laurie. Be prepared to evacuate immediately. Be prepared to stay away for an extended period of time.
He wants his mom there, and he is willing to do anything to have her there. By exiting the scene, you are allowing him to spend as much time with his mom as he wants.
If you stay and things go bad, you may be blamed for not having control of the situation.
I say "Not my Monkey, Not my Circus"