Solve This Pzzlr: Family Reunion

Neatorama presents our collaboration with Pzzlr, a site where you can always find a riddle to exercise your brain. Can you solve this one?

At a recent family reunion there was one grandmother, one grandfather, two fathers, two mothers, four children, three grandchildren, one brother, two sisters, two sons, two daughters, one father-in-law, one mother-in-law, and one daughter-in-law. Given that some people could have multiple roles, what would be the minimum number of people who must have attended, and who were they?

Try to figure this one out on your own. When you know the answer, or you give up, read the solution at Pzzlr!

Look for a new puzzle here at Neatorama every Wednesday, and check out Pzzlr for a puzzle anytime!