When I have children there will be stipulations on my side of the family seeing them, because I know that unaccaptable behavior will be modeled for them (really really excessive drinking included). No one would think you were crazy for not leaving them with a baby sitter with a drug problem, or a violence problem, etc. Why should your parents be any different?
About your own drinking, I'm very uncomfortable drinking because I have 2 alcholic parents, 2 alcholic step parents, the list goes on. Knowing that I've never really seen adults who drink in a healthy way, and knowing that addiction is often passed to children I wouldn't want to become that. It's really a decision you have to make for yourself, if you're uncomfortable drinking, you're not alone, and you're not required to drink. Why should you have to do something you're not comfortable with on what should be one of the best days of your life?