For Mother's Day, the group decides to take a family photo.
In the photo there are:
One grandfather, one grandmother, two fathers, two mothers, six children, four grandchildren, two brothers, two sisters, three sons, three daughters, one father-in-law, one mother-in-law, one daughter-in-law.
That must a total of 29 people, but no!

Question:
What is the fewest number of people that could have been in the photo?

See answer