Sui

Sarah and Harper are characters appearing in Pokémon Sun and Moon and the Pokémon anime. They are the younger twin sisters of Lana.

They appeared in Yo, Ho, Ho! Go, Popplio!. When Lana brought Ash to her home, she introduced him to her sisters. They immediately took a liking to Ash's Pikachu and started stretching his face, much to his dislike. When they saw Ash, after he and Lana walked into the room that the young girls took Pikachu to, they asked Lana if he was her boyfriend. Lana quickly denied this before Pikachu had enough of Harper's and Sarah's antics and used Thunderbolt to shock Harper and Sarah, as well as Ash, Rowlet, Lana, Lana's Popplio, and the Rotom Pokédex.
They appeared in the Poké Problem segment of SM023, dancing with their sister to the music of DJ Leo and his Alolan Dugtrio.
They reappeared in SM024 where they visited their sister along with their mother at the Pokémon School. They were excited on seeing all the Pokémon and are keen to enter the school when they are older.

(Source: Bulbapedia, edited)