My fiancé’s family HATES me

They hate me to the point where they call me names and bully me and tell me they’re going to ruin my life. They make me miserable. I have never done anything to him or them and he says they’re just jealous of me. I don’t know what to do anymore :( they make me feel attacked and hated... it just isn’t fair. ( his mother and his sister are the ones doing this) we actually have custody of my fiancé’s little brother because the mother got him taken from her. Maybe it is jealousy ... but I’m starting to be absolutely miserable and unhappy because I am being bullied.