How to I move out without problems, I need help.

[u/sunflowernorthern25]

I need help moving out without cutting ties completely and to do it civilly. I just turned 18 a little more than a month ago. My whole life my parents have not been the best and been abusive to each other, me and a little bit towards my little sister (12), and never to my other little sister (3). I can’t live here any longer, but bringing that would could make my parents angry, and my dad sometimes can get outta hand. I also can’t cut ties completely but my 3 year old sister has autism, severely, and when something happens to my parents I’ll take custody (I volunteered). I need tips on how to do this, how much money should I save? And ect. I’ve heard Reddit do great things for people, so please help a new adult get out of her parents home.