She is not the same Verity, but her and her siblings’ names were inspired by the character from the movie! I thought it would be cool to have a set of triplets named after Sinnoh’s lakes and be sort of homages to the Lake Trio. It was just an idea until Verity from the movie set in stone that I wanted them to be related to Cynthia, as the mythical connection would fit her family well. At that point, Cynthia’s family and children were already established, but I remembered that Cynthia has a sister in the games, so she seemed like a good choice. As for their father, I chose Fei mainly so that I could have the triplets share their hair color with the color scheme of the Lake Guardian they are meant to be inspired by, and also to have a legitimate mythical/supernatural connection as Fei is one of the former legendary pokémon. Amarynthia has blonde hair and Fei has blue hair and a red haired sister, so it seemed reasonable they could have blonde, blue haired, and pink haired children. Other than the premise however, I don’t really know much about Amarynthia or the triplet’s yet, sorry! I’ll share what little I do know about Verity though.
Verity is the triplet meant to be inspired by Mesprit, so she has pink hair and is probably the most emotional out of her siblings. It’s entirely possible she is somewhat similar to Verity from the movie, if not in looks, but truth be told, I haven’t seen the 20th movie so I can’t really say for certain.