I'm young and maybe dumb could you help me out?????

I'm 24 years old and not exactly sure how to handle this. The age factor is mentioned only because I always hear "young and dumb, you'll learn". Maybe thats the case here but I don't realy think so.... I have an awsome boyfriend of 4 years and wouldn't trade him in for no other, his mother and sister on the other hand..... I don't know how to deal with them. For quite some time now they have done nothing but caused problems between us! They were sending me messages on my cell saying things that aren't rite and then telling my boyfriend that I'm the one starting problems and sending them hateful messages with his phone! I couldn't deal with it anymore and confronted them face to face with him all they did was lie to him. It drove me crazy because he & I knew it wasn't true but it was like he didn't want to stand up for me! I am honestly hurt by this but he doesn't get it. Then on Christmas day they wouldn't stop calling his phone complaining about him staying home with me & our little girl. It ruined our holiday, they complained he belonged over there with them on Christmas not Christmas Eve.You see it is an ongoing problem!It hurts the both of us, not just me.Is it wrong to not do anything with them? He tells me it is but I honestly can't be around them and act fake it's not in me to do that.Will you please give me some advice, pointers,something?