I don't know what kind of relationship you have with your family, so please don't take this as advice, but a friend of ours ran into the same situation with his family. He sat them down and, quietly and calmly, said that it would mean a great deal to him if they came to his wedding and, conversely, it would hurt him a great deal if they didn't. He said they should consider that he'll only have one wedding and he wanted them to think about whether they might ever regret not having gone. He wouldn't let them say anything, and he left right after he told them to think seriously about it. They did wind up going, FWIW. I couldn't have done that, because I would never have admitted that anything my parents did could hurt me. I think he handled it better than I would have, in his shoes.