please help need advice on broken family?

[estrellita]

been with my fiancee 5y & his family are out of control they are mean, shallow & his mom favours his sister openly over him. later it has gotten much worse his sister tries to break us up, she screams at him to do things for her & his mom makes him obey, his sister has always been awful with me and has now turned his mother on me (she tells her mom i hit her, i spread rumors about her etc.. i have never said a cross word to her &for my fiancee's sake i try to be nice) my fiancee has always worked so hard to make his mom proud. he worked while traveling 4hours a day to get to uni & paying for his driving licence (he was 18) she is 26 she has had 2 scooters (he had none) she had 3 driving schools paid for her, they paid for her to go uni in england (she bailed on all of this & shes had a house built for her) and now his mom is screaming at my fiancee to let his sis drive his car! how is this fair? he has talked to them so much & nothing. he's had enough & so have i.
its not fair to carry on like this. do you think we should just cut them out of our lives now. i feel so bad for my fiancee he has tried so hard to make things right and they treat him like s.hit hes always doing things for them even while they are screaming at him because he loves them but he cant take anymore. please has anyone been in this situation what can we do? they wont listen at all & his mom says his sisters is wonderful & never does anything wrong. how did this happen & what should we do?