Even the best families can be annoying sometime, so I encourage you to do two things at those big gatherings:
#1 – When you need a little space, find a way to take it. Good techniques: walking the dog, washing some dishes, amusing the little kids, pleading food-induced need for a nap, showing the newest family member around the neighborhood, running a last-minute errand, having a shower.
#2 – Make space. Build some alone time into your events. Don't make a fuss over people retreating from time to time. Rescue the stressed.
Useful phrases include
"Mmm, fantastic. Who else is ready for a nap break?"
"I need a little walk before the pie, care to come along?"
"Mom, I can do that for you, but sit down for just a moment and tell me again about the trip where you got this vase. That was just after you two got married, right?"
"Okay, that's got about an hour more to cook and everything else is all ready, so you all can just relax or read or whatever and I'll let you know when we get close to dinner time."