Yes! I have done this before and I am doing it again next week. It'll be me, my DH, my DD, my sister, her DH, her 3 kids and my parents for a total of 6 adults and 4 children ages 1, 2, 2, & 7.
My biggest piece of advise is to do your own thing and let them do their own thing. For instance, if you are EE folks and they are not ... don't make them get up early or wait for them to get out of bed. One or both of you will wind up frustrated. Instead, arrange to meet them at the park. Make a couple of PSs for dinner and lunch. Be prepared for them to deceide that they don't want to go to some of the places you have planned (even if they OK'd it before).
What I do is plan a bunch of PSs, plan my days and then tell my family if they want to join us that's fine. If not, that's fine too.