We are engaged after eight years together and want something very low key. We looked into eloping but those wedding seem more expensive so we have decided on a small registry office wedding followed by something nice after, like dinner at a nice hotel.
We only want to invite a few people - my nan, my parents and his parents. One of my sisters is living in New Zealand so won't make it, and my other sister may get an invite (haven't decided yet).
The issue is my fiancé's brother. In our whole relationship I've barely had a conversation with him as he's always in his room playing xbox or smoking weed. He's always ignored me, apart from one time he made a 'joke' about me calling fat 
he was only 15 at the time but I really took it to heart,
He is a stranger to me and I would feel awkward having him at our small and intimate wedding (my sister and parents have always made an effort with fiancé and know him quite well and same with me and his parents).
I've told DP I'm not too keen, and doubt his brother would want to come anyway. But he still wants to invite him but probably would keep it to just his parents if I insisted. I would probably have to not invite my sister either though so this would look acceptable. I know I'm probably BU but it would make me feel embarrassed all dressed up in my wedding dress and saying vows in front of a stranger really, who insulted me all those years ago.