We do a family vacation every year. Grandparents, parents (us), kids, cousins. Lots of possible activities - biking, swimming, boating, golf, hiking, mountain biking (for grown-ups), mini-golf, date nights, family game night. It truly is a challenge to coordinate the activities of 6 adults and 5 young children and then add in another 8 adults and 3 kids on the cousins side and also friends who love in the area.
Last year I took a white board, and we mapped out the week. They all thought I was crazy, but it worked. Major stress reducer. Everyone got to say what was important to them. We put it all on the board. We did all the most important activities and even most of the nice to dos. A little planning goes a long way and makes everyone feel like they had input and could understand why we did what we did. And it made it clear why we were going separate ways sometimes.