my parents HATE my bf help

So my bf is 21 and I am 17. I know him because he is my brothers girlfriends brother which yes I know isn't the most normal of situations but my mum and dad hate him
They are the type of people that if they don't like someone they will show it and they show it to him, he will wave and say hi when he's picking me up and they will blank him
I don't know what to do because I'm stuck in the middle of it all 
Now there's a family party and he was invited by my brother but he doesn't want to come because he thinks it will be awkward between him and my parents 
What do I do to resolve this