You are in the same boat as my H and his sister. They have nothing to do with their mother...she has figuratively stabbed them over and over again.

I literally have the MIL from hell. I knew it was bad when the first (and only) time I went to her house, she asked my SIL to hand her a pistol. When SIL asked why, she said, "because I want to point it at her (me) and make her one of us."