What plant family do grapefruits belong to?

Grapefruits belong to the family Rutaceae (roo-TAY-see-ee), also known as the rue or citrus family. A defining characteristic of the Rutaceae is its fruit. The botanical Word for a citrus type fruit is "hesperidium". Not all plants in the Rutaceae have hesperidiums, but all plants with hesperidiums are in the Rutaceae. Another common characteristic is the presence of fragrant and stringent chemicals in the leaves, stems, and other parts.

Grapefruits have nothing to do with grapes ;) Grapes are in the grape or vine family, Vitaceae.