Balei grew up in Poni Island in Alola, she stayed there up until she got her scar and then she moved to Malie City, this is where she lived for the rest of her life!

Back to Poni Island she lived a pretty chill life in the Seafolk Village save for the trainer pokemon incident, she spent a lot of her youth climbing and exploring around the Vast Poni Canyon. Living in a town of boat houses made her appreciate the waters as well, sometimes she would go diving and collect shells!
TL;DR: She had a fun childhood full of adventure

Jasmine: She basically grew up on a hospital Due to a serious illness, However she still remembers that time fondly, thanks to the nurses and doctors, and visits the hospital from time to time

Andres: His Parents passed away when he was really young so he started to live with his grampa which had a strict but fair house policy. Andres really admired his grampa and strives to be like him

Mary grew up in Hammerlocke on her family's estate, she enjoyed a peaceful if not somewhat strict upbringing as the heir to house Enett.
Jin was born and raised in a secluded martial arts school in the wilderness of Sinnoh's Battle Area, she enjoyed a great bit of freedom while also training from a young age to master her abilities to sense and manipulate aura.
Celeste grew up in Nacrene city with her family, she had a pretty normal childhood.