Use a Relative's House
Dorothy just might have been on to something when she tapped her heels three times and repeated, "There's no place like home." Hosting the family get-together at a relative's residence can really make other members feel right at home.
So how does it work? Find one person with a house big enough where everyone can stay or use the home as central headquarters. Central headquarters is the place where people meet up between activities, check-in when they first arrive or go to chill out and relax. If the host home isn't big enough for everyone to crash, the host can find a hotel close enough for some of the relatives to commute to.
Daily activities could include a picnic lunch at a local park or in the host's backyard, an outdoor sporting competition or indoor gamefest, followed by an evening awards banquet at the hotel. After the meal, get ready to clear the tables while Aunt Gladys kicks off her stilettos and runs to the dance floor for the Electric Slide.