Misty's Sisters from the anime – Lily, Violet, and Daisy – appear in Let's Go! Pikachu and Let's Go! Eevee… technically.
The three gym trainers in the Cerulean Gym are named after the sisters. They even kinda have the same Pokémon. In the anime, the sisters use Dewgong, Shellder, and Seaking. In the games, the trainers use Seel, Shellder, and Goldeen.
The technical part of this post is that it is unconfirmed if the gym trainers are related to Misty or each other in Let's Go! Pikachu and Let's Go! Eevee. So take it with a grain of salt if you want to believe that this confirms Misty has siblings due to the games' dubious canonicity. Even then, it's a nice nod to the anime besides Jessie, James, and Meowth showing up.
by Ecla1r_