Parents are really threatening and make good on their threats . I'm from an oriental asian background, it's the norm for parents to hit their kids. I'm also 18, a legal adult and I've threatened my own mum, pretended to call the police but one word from her in that threatening tone shocks me to not do anything because she's actually so scary.
Doing anything against it, fighting back ends up with more pain for the kid and everything only gets worse.
For OP to move out, it'd need to be done very quickly, all the stuff organised and then move out completely within a few hours when the parent isn't home and then completely avoid the parent for a few weeks not days for it to calm down a bit. No going back if someone is forgotten because she'd get caught.
I've also got siblings and I have to defend them, block the hits so my parents just beat me more to make up for me not letting them beat my younger sibling because they can't get their frustration out on who they initially wanted to.
I won't be able to move out unless I can take my younger sibling with me because then all the anger and frustration would be taken out on them and I can't bear them to be in pain.
Completely understand how OP feels.