STBXAH has suggested collaborative parenting. . .and I think it is a good idea. But he needs to step up to the plate and protect his son, not harm him.
Well, he's proven that he's not going to do that. Expecting this of an active alcoholic is unrealistic, and is only going to hurt your son more and more as his disease worsens.
I don't see anything here that is a good idea -- shoving, shouting, pinching, threats, in addition to having to watch him get raving drunk and feeding your son to relatives to abuse too?
The real question is not who loves who but what are you going to do to protect your son? Have you documented this and reported all of it to your attorney? This is child abuse, and you do have the power to not let this happen again. But if you don't report it, you're just standing by and once again expecting AH to do the right thing. Sorry for my tone --- but I had a mother who would not protect me because she lived in a fantasy world about how my father really WAS - and didn't want to make waves. It took many, many years to heal from that, and in some ways I never can.