Harper and Sarah 'Opunui

Hannah Aleka 'Opunui (nicknamed "Harper") and Sarah Suiren 'Opunui are twin sisters from Hau'oli City on Melemele Island in the Alola region. They're the little sisters of Lana 'Opunui, although there whereabouts are currently unknown in the series.

Background
The 'Opunui family was already mildly struggling financially, but Lana's parents figured they can afford the expected child, since the wife was pregnant. However, after further tests, it was revealed that Lana's mom was having twins. This shocked her parents and kept them uneasy. The twins, Hannah ("Harper") and Sarah, were born and Lana loved them dearly. She enjoyed playing with them and was a major part of their early infant days.

When Harper and Sarah were 2, however, it was ultimately decided that Lana's parents couldn't afford 3 children instead of 2. They gave up the twins to a foster home. Lana was furious at this and had begged them for weeks not to do this. When it was done, Lana was extremely upset at her parents and couldn't find it in her heart to forgive them. Alola doesn't have a foster home, so the twins were sent to a different region. Knowing the foster home system, when one home can't maintain a certain capacity, children might be sent to a different home at sporadic times. It's assumed that the twins are in a foster home now in a region unknown to their parents or Lana.

Present
Harper and Sarah haven't debuted in the series yet. They were first mentioned by Lana in Episode 31 when she told the Mokusetsu about herself. She mentioned about how the twins were given up by her parents, which had infuriated her. Mallow aided in telling them that Lana is living with her and 'Ulu, due to how upset she was with her parents. Lana mentioned to them that she doesn't know where her little sisters are, but that she misses spending time with them.

Harper

 * Her first name, Hannah, is her name in the German dub of the Pokémon anime. The German name was decided, due to it being the closest to her English dub name, since Jay wanted "Harper" to be a nickname.
 * Her nickname, Harper, is her name in the English dub of the anime.
 * Her middle name, Aleka, was randomly chosen from a Hawaiian name generator.

Sarah

 * Her first name, Sarah, is her name in the English dub of the Pokémon anime.
 * Her middle name, Suiren, is actually the Japanese name of Lana in the anime. It comes from "睡蓮 suiren", meaning "water lily" and also from "水 sui", meaning "water".
 * Also, Sarah's Japanese name happens to be "Sui", which, again, means "water", and it also comes from "放水 hōsui", meaning "water spray".

Other

 * Their last name,  'Opunui, is shared with Lana. It was randomly selected from a Hawaiian name generator.

General

 * Their birthday, December 1st, is the original Japan air date of the episode of the Pokémon anime they debuted in.