Thanksgiving Dinner

Susan has invited her family to Thanksgiving Dinner. As her plates are not the best, Susan wants to buy new plates, one for each person at her Thanksgiving Dinner.

There'll be a grandfather, a grandmother, 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 a daughter-in-law.

At least how many plates does Susan need to buy?