Fiances ex-gf living with his mom?

They lived there together when he was with her but when they broke up she never left. It bothers me a lot, especially since I'm expected to partake in events there and have a relationship with his mother. His ex doesn't like me and I have attempted to be her friend in the past. She has been rude to me and has always blamed me for her and him not getting back together when they broke up. His mom is alone a lot so she doesn't want his ex to leave because of this. I have told them time and again that I would be closer and visit more if the ex wasn't in the picture. I really do want to have a relationship with his mother, she's a great woman but I feel like I will never be a true part of this family if she is in the picture. My fiance has expressed his disapproval with her living there still but nothing has been done. He feels he can't do anything else to change it. I don't feel comfortable around her. She has started rumors in the past about me as revenge and she's always odd acting when she runs into me. I feel tense in this situation but there is nothing I can do about it it seems. His stepfather wants her out too but him or his mother doesn't want to put her out. She has family she can stay with but she refuses to do that. She takes advantage of living there for free and being so close to work. When I requested her not be there for my first Thanksgiving with my fiances family she responded with "I shouldn't have to leave MY house for them to come over, they can just DEAL with it". Any advice on how to cope with this situation? It would be appreciated. Thanks!