The simplistic way to style your photo-shoot, is to visualize where your image will be placed. What season do you want to have on your wall/display tables? Holidays can be too much for everyday style, or winter scenes can be tough to look at in the heat of the summer, the choice is yours.
Questions to Ask:
Multiple Families: Have the families pick their favorite color. Have a (1) common theme with all the families example pants/shirts.
Do we have a matriarch(grand-parent) that person should be the prominent color & different from all the rest.
Single Families: The same theme applies from the multiple families, except the head of the family/parents should be prominent. Children can be complimentary colors.
Further Questions can be directed to your photographer...