My brother in law is threatening suicide, what should I do?

I had my BIL down on Monday he was actually down to speak to my husband outside in the car but eventually came in so he cold wash his face, he was in a pretty bad way and its because of my mother in law. Apparently on Saturday night he was at his girlfriends house when my mother in law came to the door demanding his house keys (he lives with his mum) and his mobile phone (the phones in her name) when he gave her these items she then proceeded to punch him in the head and try head him twice!! This is all because she does not like his girlfriend the girl has at one time been with another woman and since decided she is straight and started a relationship with my brother in law but my mother in law doesnt like this and calls her and that he is balckening her name by being in a relationship with her. After all this he is really down he is saying there is no point in life and he wants to jump in front of a train and just end it. I am very worried as you can imagine. Especially since my husband has been through all this before him she kicked my husband out of her house if i didnt let her see my daughter, her granddaughter whenever she asked she also made me and my daughter unwelcome in her house and threatened us with the social services when we said she couldnt have her on a certain day as we had plans! My Mother in law has also threatened violence towards my husband, What can be done about her? How do I get her to see what she is doing to her sons? And finally what do i do about a suicidal brother in law? Im sorry this is long!!