I'd walk away from the family, except your sister.
I agree, your lucky to have a twin. Stick together and forget the others. Your young and there is a whole world out there to explore. Someone once told me no one can control your emotions unless you allow them, be strong believe in yourself and enjoy life. Abuse is not tolerated.
Thank goodness you are adults! I say walk away too! You don't need that. They sound like horrible rotten scoundrels who don't deserve to be a part of your life. Even if you were biological children I would say the same thing.
Drunk people do and say things that they don't mean to make themselves feel better. They terrorize people because they have bad self esteems and they think everyone else is to blame for their problems/bad self feelings. It's not worth sticking around. Nothing they do are say is accurate, and almost everything is intentially hurtful.
I say, you and your sister write them out of your life and move forward. If you are close to aunts, uncles, grandparents, then keep them around for support. If extended family is sober and they know how your dad is then they will most likely support your decision. If they don't support you, it will be hard to walk away, but in the long run I think it would be for the best.
Just make sure to find friends who will support you and be a shoulder when you need one.
Good luck to you two!
If it makes you feel any better I feel like I sort of can relate. My adoptive family is just fake. They talk about caring but actions speak louder than words and trust me they don't act like they give damn. I always wonder what it'd be like to have been adopted by someone else. I am a recovering addict so I am very familiar with addiction. Your dad has to really care and want to stop. I am sorry they treat you bad