We did this a few weeks ago with extended family. Not a beach house but by the bay and with a swimming pool. 10 adults, 8 kids (5 below 4 yrs). There were also daytime visitors too -5 adults. It was great fun!
The swimming pool was a great saver and lots of fun. There were always issues with Food and Cleaning were always. Kids had issues with allergies. There's always someone that will not clean or cook...unfortunately, that person was the one who complained the most too and didn't get up till 11am AND napped in the afternoon. AND complained that we went to the pool without her. Always 2 steps behind everyone.
Even with some issues, we all want to do it again next year. oh lord. help me. I was the organizer.