Any two people. Could be just dating, an engagement, an anniversary, etc.
Photographs for businesses, magazines, online publications, bloggers, products, brands, etc.
Celebrating the blessing that is pregnancy. Usually done when the belly bump has "popped."
Hospital or at home session with mom, dad, and baby within the first 48 hours of the baby's birth.
Mom, dad, & kids; grandparents with grandchildren; generational photos, etc.
There is no limit to the number of people you can have in family sessions - the more the merrier!