OK, I get that they are excited, but like PP said, if you don't stand your ground and start building some boundaries now, you never will. You and your husband are adults, however, you are allowing your families to tell you what to do. Say no, end of story. What is really getting to me is in the other thread, you say they all want to come to your u/s appointment and your only reaction is ugh, like it's going to happen because it's what they want. If you don't learn to stand up for yourself now, these people are going to be telling you how to raise your child. Sac up (seems to be my favorite phrase today, but it's appropriate).
It really bugs me when people use the "it's the 1st grandchild on both sides" as an excuse to let their parents run roughshod over their lives. Guess what, Li is the first grandchild on both sides in our family, too. We made it very clear that we are her parents and everything is our decision, that included decisions being made while I was pregnant (which included hands off the belly). Did everyone like it, no, but, it's not their call. Their job is to spoil the heck out of her, but if DH and I say no, that is the way it is, no questions asked.
If you don't want this party, stop aiding in it. Stop making a guest list, don't go to "meetings", tell them you don't want it and aren't going to go. This is your life, you have a say in it.