I'm going to try to make my father and step mum break up
Why do you want them to break up?
I don't like my step mum and don't want to have to see her again.
It's understandable to dislike your step mum, but you shouldn't try to cause her and your father to break up. Meddling with someone's relationship, especially your parent's relationship, is not appropriate.
I'm going to make sure she doesn't live in my house ever again.
Breaking these two up will make them both upset at you and your father will be quite frustrated. You should want your dad to be happy and try to get along with your step mom.