I agree with most of the above....we did this last Easter, there were 3 families with 10 altogether. We discussed what things we would be doing that everyone wanted to do (we did a day at Universal, a day at Knotts, Medieval Times, and a day in Santa Monica. All of those things we planned for in advance. Apart from that and a few meals, we started out the trip together until everyone had the hang of how the parks worked, then each day everyone did their own thing, sometimes we met up or mixed groups, sometimes we ended up on our own. Best to keep communication open, but don't expect you will spend all your time together, and I'm sure you'll have a great time.