My 5 years olds family??? help?

So i got pregnant when i was 18 by my BF at the time, long story short he was a junky and ped away of a heroin overdose when she was 1 1/2 old. she was always my priority in everything i do, and still is. i never brought guys that i dated around her till now, i met the man i'm engaged to about 3 years ago now, where getting married in Nov 2009, she was about 3 yrs old when she met him, and they both look more alike than her and i. i know crazy huh? anyways she has no idea that he is not her dad, he treats her as if she is his, supports her financially, mentally, physically, ect. we added another addition to the family another girl who she loves and adores, she's a wonderful big sister. the problem i have is with her "real dads" family, he has 5 brothers, and obviously their mother, my daughters grandma. at first they supported my relationship, and then they where threatened by it, and telling my 3 yr old at the time, that he wasn't her dad, ect. showing her pictures of her "real dad" whom she has no clue about. it's been 2 1/2 years now, and i will not let her go anywhere with them by herself, the grandmother is very controlling and likes to put her 2 sense in where it's not needed or asked. i'm almost to the point where i just want to cut all ties with them, they cause problems with my daughter and her security, and also my relationship, it's very hard for my fiancee to continue to be her DAD, when she comes home and says hurtful things that they tell my daughter, and when her behavior changes so radically. am i doing the right thing by not letting them see her? or will she hate me later for keeping her from them?