I talk to a lot of photographers. I read a lot of things photographers write, and I've noticed that extended family photo sessions are not popular. Photographers don't like them because it's a bit chaotic and stressful. When there are so many people together it isn't always easy to bring them all together. I'm not sure if it's because I come from a really big family, or that I'm a bit crazy myself, but I love the big groups. The chaos doesn't bother me. I love it when you can see an image (like the first one here) and see a bit of everyone's personalities in it. It's not perfect. It's not the traditional everyone smiling for the camera photo, but it sure does show the personalities of the family. I like how genuine it is.
If you are booking a session with a photographer for a large group my advice to you is to be flexible. There will be at least one child who isn't happy. There will be adults who are not excited about the idea and are grumpy. Let the photographer worry about it. You just do your best to relax and keep the mood light. Don't punish your threaten the children. That just causes more stress. Joking around and making everyone laugh is a much better way to go.
This family had the right attitude. They worked around the not so cooperative child and made it work. Patience and flexibility go a long way when that happens. It was a fun afternoon on the trail on a beautiful day in Southern California.