Cant cope with fiances sister

Needhelp101

My fiances sister is driving me crazy. For as long as iv known her she has had some sort of problem with me which i dont understand as i have never done anything to her ever. It started when we were first dating i was 18 and he was 21 and living with her and her two daughters at the time. (She had seperated from her cheating partner). Shed constantly make dry remarks or her daughters who were younger would come ot with random insulting things to me like of i as much as had a pimple on my face they would point it out in a room full of people or ask my why at the time i like wearing tracksuits. She would never correct them or say thats rude just smirk away at me while i was pure red in the face with embarrassment yet she would cprrect them over less. Then there was the fact that my fiance and her had lets just say a very weird brother sister bond to me anyways. Dont get me wrong theres nothing bad about having a clpse brother sister relatioship but theres was just odd like o came into the house one day to picm him up and he was sitting on the couch watching tv and she was practically lying across him with her feet stretched out across him which i found extremely weird and felt uncomfortable which i stated to him but he didnt see any harm in it. Then there was the fact she was constantly making him babysit and putting a guilt trip on him of he said he couldnt do it because we were busy, shed act lile as if he was the kids father that was refusing 2 spend time with them. Then there was the fact that he used to confide in her with everything including personal issues in our relationship which i also found wrong like for instance long before we had our son whos 3 now, i had a pregnancy scare and he told her all about it which she got great pleasure in saying to my brother and sister at a family event. Theres so much more that she has done to us but its just too long to get into, however whem my son was 6 months old she nearly got us to break up but we patched things up and my fiance swore he would never tell her anything again. Fast forward present day and she still trying to interfer and get involved this time in the wedding plans. She even flipped out on my fiance because i didnt ask her to be bridesmaid..lol.. now she wants him to stay in her house the night before our wedding instead of his parents house just because she doesnt talk to there mum over a petty arguement and is trying to play the guilt trip card on him which is annoying me. She is currently dating a man that lets just say is not anyones cup of tea my family hate him, the rest of my fiances family hate him and both me and my fiance dont want him at the wedding but my fiances too scarde to say it to her incase of her reaction. Its like she still has some sort of strange hold on him even though we keep our distance from her. I dont know what to do with her its really getting to me i need advise to handle her properly because my fiance seems to be both too soft and scared of her to have it out with her.