.. and the easiest way to tell them apart is their fashion.
History gets the most notorious 2 Victorias and the 2 Eugenies confused a lot, but you can tell by their clothing which one is being discussed. Each went through a specific fashion era, and it helps that they were all very fashionable and up to date with the most current styles.
(Portrait: Dowager Empress Eugenie of Spain, goddaughter of Queen Victoria & Granddaughter of Empress Eugenie of France, with Queen Victoria of England in about 1915)