As far as rey goes….does doesn't know want the force is just like she had no recallection of her past or parents.
My theory is that she was one of Luke's trainees at his Jedi Academy. She had visions of kylo killing when she gets to the basement where Luke's light Saber is. I assume she was a trainee and possibly blood related to luke somehow. Luke hides her on jakku an outter rim planets that the first order doesn't give a shit about cuz it's a lame empty planet. Outter rim planets also don't have a ton of people who are force sensitive so it's easy for them to hide her there with that old man who died at the beginning to watch over her presumeably to give her the map to luke once she's ready.
I also assume she's somehow related to luke cuz R2-D2 was dormant for years and powered on with her presence. I have more of a problem with how Finn a storm trooper could hold his own with a light Saber against kylo