NTA - I too went through this but reverse roll and it was my dad. I’m one of 4 as well. Sometimes when therapy doesn’t work, when speaking nicely or coming up with solutions doesn’t work you just blow up. That one last ditch attempt at getting through to them. Changes for a bit then goes back to what they find comfortable. They’re broken and they refuse to be fixed, it’s all on them to fix it, not you.

I ended up providing my siblings an alternative role model. I fly them for holidays, buy them birthday present and my sister who is close in age does the same but as a mother figure. Sometimes if you want to see a change you step up. I wanted to be everything he wasn’t and I make that my life’s mission.

Best of luck OP, I hope your future is happier and more fulfilling.