I'm not inviting my brother to my daughter's wedding because he's gay
Why wouldn't you want him there just because he's gay?
It'd make the other guests uncomfortable
It sounds like these other guests of yours need to get over it! Nobody should be excluded from something just because their sexual orientation is different than others. You should let him come to the wedding.
It's a big no. I don't want him there.
Don't think you think your brother will be really sad about this? You should invite him, he's family and his sexual preference doesn't change that.