My mother remarried a man who has extreme anger issues when his young step son makes a mistake he threatens him by saying, "i'll beat you!" Or "i'll break your arm" i dont live in the house, they sent me away but i was wondering if an older sibling could get custody of me
Probably not. The older sibling would have to be able to support himself and you. Also, the older sibling would have to have standing, which is the right to sue. If your mother has sent you away your father should try to get custody of you.