Why they act immature?

I went to a party and 2 of my cousins were there..we use to be so close but I have no idea what happened..there best friends one is older then me by 4 years and I am older then the other one by 4 years.. They look at me so weird..they don’t talk to me people think there so inncoent..they are rude, curde and playing stupid…it was one of my cousin party I was in her room and she came and told me “move, I need to change..then I went to another room and the other one came and said “can you leave my lil sis is gonna take a nap..I don’t want any trouble but the fact they act like I am there enemy when we use to be friends and all of a sudden they don’t talk to me and they dog me kills me..girls tell me there jealous but I don’t think its ture cause I know there waaay prettier then me..one has her hair blonde up to her behind like me and the other one has long black hair to the thights..and I here them saying I have longer..shiner..skilyer hair the her..I am and no competetion..one of them likes this guy that I like years ago when she can freakn have him..what should I do we go to parties like all mad at each other acting we didn’t c each other there always against me and please don’t say talk to them cause I don’t kiss a$$..