How many did medusa have sisters?

Medusa had two Gorgon sisters - Sthenno and Euryale; her other sisters by her mother Keto include the three Graiai: Deino, Enyo, and Persis and Ekhidna the "mother of monsters", and Skylla who in classical art was depicted as a fish-tailed sea-goddess with a cluster of canine fore-parts surrounding her waist.