What if I just never speak to my father and his fiancee again?
Why don't you want to speak to your father and his fiancee?
Because he's not treating my mom right and I hate his fiancee
You shouldn't ignore your family, even if they are making you upset.  It's understandable that you do not like your father's fiancee, but you cannot let her get between you and your father's relationship.  You should talk to your father about the situation, and if has any respect for you he will listen to what you have to say and make some changes.
Maybe. I think I'll just ghost them for a bit
It's okay to give yourself a break from people that have bothered you, but you should always eventually speak with your father again. People are typically expected to be on good terms with their mother and father, and it is considered weird if you aren't.