Big families are fun, noisy, chaotic and depending on your mindset, the politics can be interesting to negotiate too. I am glad my wife has a large extended family, which provides a very favourable and loving environment for my two kids to grow up in.
That's why I have a personal bias towards shooting a big family. The dynamics can be very explosive because my usual number subjects gets multiplied by sometimes a factor of 10. At the same time, the energy pervades throughout the session, making it very rewarding too.
I usually leave the posing to the family members if I sense that they can manage very well on their own. I let the individual family's character emerge, and the difference between various nucleus families can be very fascinating.
Contrary to conventional belief, having a "mass shoot out" does not dilute the quality of the photography each family is entitled to. Instead, the presence of all the other family members serve to either encourage one to "outdo" the other in a good-natured "rivalry", often shrouded in laughters and wolf-whistles from those off-camera.
Another advantage of a big family shoot is the cost. A session fee of $500 divided by 6 is less than $100 per family. What they get is a lifetime of memories, and some kickass family portraits.