My uncle is exactly the same as your father. And I mean exactly, and I'm ashamed to say my family never did anything to protect his children. Now on of them is a herion-whore at best or death at worst and the other is in a psychiatric-institution.
I can't really give you much advice, but I can tell you two things about people like your father and my uncle.
First they can't be trusted, and are very hard to touch by the law. Me most likely knows very well how far he can push the law, and he will push it to that extent.
Second guilting them into doing anything doesn't work. In their screwed up little version of the world they are the most wonderful people and everybody is out to get them. From their point of view the have the worst luck and the toughest lives.
You really need to seek help from professionals. Sorry that I can't give any better advice.
