Problems with SO family :(

Okay so me and my boyfriend have been dating for almost 3 years now. He's Muslim and I'm Christian which isn't a big deal to us because nether of us are that religious and we accept each other and our religions and enjoy that we have that to discuss and compromise on. HOWEVER, his family can't stand me. I've never met them really just his two sisters and on accident at that, his younger sister of the three love me but the older two can not stand me and I've never met them!!! They post mean shit on his Facebook when there's a picture of me and they say mean nasty things to him. They also pass this on to their mom who doesn't have a problem with me but still has not met me! Me and him have been arguing like crazy about it because I want him to step up. I'm not allowed at his apartment in fear of one of his family members coming over. He never stays the night in fear of them finding out which means he also is afraid to stay out too late with me. He had them blocked from seeingn anything I tag him in on Facebook as in pictures and stuff because he doesn't want them saying anything but at the same time I just am at the point where I feel he should stick up for me and suck it up??? Am I wrong???