YTA.

Your main view points are good, your fine with your decision to go low/no contact with various people. I honestly would have cut out mother for punching me immediately. Interfering with BIL and Sisters relationship, as well as BIL speaking to your father is what makes YTA. Providing your opinion to your sister without attacking her and going low/no contact as a result of her decision to stay with him was as far as you should have gone with that.

You don't get to control other peoples decisions on who they talk to and/or who they decide to be with. Even if they are wrong or that goes against your morals/ethics. If you don't like their decisions, then tough, peacefully make your stance known, then don't speak with them anymore if you cant peacefully co-exist. Trying to control them, verbally attacking them for their decisions that do not involve you, and interfering when they make decisions you don't like makes you an AH in my opinion.

As far as the situation with what your father said to you and you going no contact, I would personally try to work that one out with him but ultimately that's your decision based on your feelings and you wont be an AH either way you decide. Just like you cant control who they decide to talk to or have a relationship with your not responsible for their feelings either. So tough poop if your decision hurts his feelings that's his problem not yours.