LOL. There is no right answer to this one. First of all, your baby will be unpredictable. You have no idea how stimulated he will be with the voices, lights, and activity. When we had to take our son to a family wedding when he was 7 months, old, we just went with the knowledge that we would have to leave whenever he couldn't handle it any more. In general, people loved holding him and carrying him around. He hadn't hit separation anxiety yet, so he was okay with it. He had fallen asleep on the way to the reception, which we hadn't expected, so he slept through half of dinner.
I think whatever you choose is fine, BUT let the family know that you will leave if you deem that it is best for your son, and that you hope they will be understanding and enjoy themselves.