Hi Robster and WELCOME to SR. I'm glad you found this place. There's lots of support to be had here.
Seems to me that you are going to have to protect yourself and your children from your ABF. You mention physical abuse...has it been reported to the police? Have you documents all the events where abuse took place?
IMO, it's time to talk to a few lawyers and get the ball rolling on securing custody and separation. Your ABF sounds unstable and his family will be of no help to you whatsoever.
*hugs* I'm sorry you in this situation, but I'm glad your search lead you here. SR is a great place to be.