I'm sorry you're going through this with your dad, and your sister. I mentioned here in AO last year that I had similar feelings of frustration with my father, and wanted to get some distance from him or possibly cut him out of my life, and currently I am exercising that distance. I am not talking to him or seeing him, and everyone in the family is aware. Initially there were questions of concern and frustration and people wanting to understand or try to reconcile, but I held firm to what I needed to do for me, and essentially told them they can respect it or leave me alone too. Surprisingly, it's been going okay, but I also think there is an expectation that this is temporary, especially because I haven't explained anything to him really. Honestly, for me, I don't know if it is temporary or not. The odds of me spending time with him only for him to do exactly what you described happened to you just seem so likely that it doesn't seem worth it. Yet, I also feel somewhat pulled in by this 'family loyalty', which really for me is just showing up as fond old memories of good times. If I do decide to re-engage with him, I know I would need to do some thinking for myself on what kind of expectations do I have for the relationship moving forward, what are my boundaries, what can I tolerate and what can't I tolerate. I also would want to communicate with my dad at least some of that, so that he's aware that for me the relationship can't be the same as it used to be, and that it caused me too much pain and frustration, and that if he cares to keep me in his life then it will take work from both of us. But, ugh, I don't know if he's capable, and I just really don't know if I have the energy to do that work with him.
I have cut friends out of my life before, though it has been a while. It's never easy, but it does feel easier than with family and all the family entanglements. I never have felt any sort of regret or remorse for saying goodbye to a friendship when I do finally make that choice to let go. I've never gone back to a friendship that I've ended (except for once in high school but that was a messy, dramatic, toxic friend group peer pressure situation that I ran far away from the moment we graduated). Some - arguably, most - people are not meant to be in your life for your entire life, moments can be treasured just for what they are without needing to be stretched into forever to be meaningful or important. So, I choose to be grateful for the positive things I gained from the friendships, recognize they no longer serve me, and let them go. As Ariana Grande says: Thank U, Next. :)