Abusive father

I'm 20 & currently live w/my folks. My dad's been increasingly verbally abusive over the last few months and obsessed in a delusional religious hate group. My younger sister has simultaneously been becoming more and more manic & depressed & paranoid. The abuse escalated into physical abuse and my mom made my sister lie to a doctor about her head injury. My sister is terrified of him. My dad has agreed to move out, though he doesn't consider his behavior abusive & tells us we're crazy. My mom's also looking at apartments so we can move if he's not quick enough, and we're goin away on vacation w/o him in the meantime. I'm not sure what the next few weeks will be like, just taking one day at a time & I need to be solid for my mom & sister. Any advice, stories, whatever you've got would be appreciated. I know things will get better but right now I'm just angry and anxious. Also I know I shouldn't bit I feel guilty cause my dad needs help, too & he's just gonna get worse as he pushes more & more people away but I know he's never gonna want help