Kinship puzzles, like age puzzles, are problems to do with how family members are related and go back many centuries. Some of them can be fiendishly convoluted, especially if incestuous pairings are allowed (in the puzzle!). Sketching a genealogical tree is sometimes helpful. The following all involve legitimate ties:

 

1. Brothers and sisters have I none, but that man's father is my father's son. Who is that man? (This is one of the oldest problems of the kinship variety.)

2. What is the simplest way in which two people can be an uncle to each other? (From Dudeney's A Puzzle-Mine)

3. A certain family party consisted of 1 grandfather, 1 grandmother, 2 fathers, 2 mothers, 4 children, 3 grandchildren, 1 brother, 2 sisters, 2 sons, 2 daughters, 1 father-in-law, 1 mother-in-law, and 1 daughter-in-law. Twenty-three people, you will say. No; there were only seven persons present. Can you show how this might be? (From Amusements in Mathematics.)

Solutions

1. Your son.
2. Sons of two men who married each other's mothers.
3. The party consisted of 2 girls and a boy, their father and mother, and their father's father and mother.