one of the obstacles many spouses who think of leaving have to deal with is feeling like they are somehow ABANDONING their partner. well good news, your AH has his family, so you can just X that concern off your list. and focus entirely on taking care of yourself and your child!!!
leaving is a process - yes, there is the option to simply run out the door screaming, or sneak out in the middle of the night, and for some that IS the only safe option. but in many cases, it's a matter of crafting a plan, a solid well considered and well adhered to plan. getting proper legal counseling is essential, so that you don't make any missteps that could come back to bite you later.
i'd also suggest you keep this to yourself - not share with AH or any of his familia. no threats, no OR ELSE's, no giving him one more chance so that you can hold off on action.