My boyfriends mother and sister hate me for no reason what can i do?

My boyfriend and I have only been going out for a couple weeks but we were best friends before we went out so were totally into each other. The only thing is that the whole time that him and I hung out as friends his mother thought I lead him on so she didn't like me. I was find with that and I could totally understand it, but now its about a month later and she still is acting rudely towards me. I just want her to like me. And its not just my boyfriend mother its his sister too. His older sister is about 19 and shes the biggest fake ever. When i first met her as a friend I thought she was uber sweet and the only one who made me feel welcome at his house. However, after I talked to my boyfriend for a bit she totally hates me along with every other person he ociates with. I haven't done anything to her and it's just so upsetting. Am i really that bad of a person or do they have no reason for reacting like this? What can i do?