The Delaney sisters were Human twins, Jenny and Megan.
They were assigned to astrometrics aboard USS Voyager when the starship was pulled into the Delta Quadrant by the Caretaker in 2371.
Tom Paris and Harry Kim dated them briefly before becoming good friends. They also joined the two in Paris' Captain Proton program as The Twin Mistresses of Evil. (VOY: "Time and Again", "Prime Factors", "Thirty Days")
In 2374, B'Elanna Torres stated that Kelis would have to do better than having Harry Kim kissing the Delaney Sisters in his play in order to appease his patron. (VOY: "Muse")
A deleted scene from "Thirty Days" would have revealed the sisters to belong to
Voyager's science division. A Pocket VOY novel further narrows it down to the stellar cartography department.