Good advice for dressing for a family photo shoot from a blog called Tiny Twig goes out on a limb.


Pick 3 colors to work from.  Make 2 colors the "main" colors and throw the other in "pops" for variety.  
Mix in some prints and patterns for interest.
Vary the lengths of pants, skirts, and dresses.
Make sure members of the same smaller family unit are not wearing the same tone and hue--they will blend together when standing next to each other.
Take each person's personal style into account.