A FAMILY PARTY

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?