The Triton cousins refer to the sons/daughters of Cilan, Chili and Cress, the former gym leaders of the f Striaton City Gym.
Emery is the son of Chili and specializes with -types. His prized Pokémon is a female Frillish.
The youngest of the three cousins, Delaney, is the daughter of Cress and specializes with -types. Her prized Pokémon that she uses is a female Purrloin, much to her Uncle Cilan's dismay.