What do I do about my boyfriends son?

What do I do? My boyfriend's son is 15 and makes things so difficult. He doesnt seem to care about other's feelings or how he treats others. He's awful to me, my boyfriend, and his sister. My boyfriend and I share a 3 year old, who he is great with; but he makes life miserable for the rest of us. I know its not my place to law down the law, but I feel like my boyfriend let's him get away with way too much and that's why he acts the way he does.. any advice?