There are plenty of stories that can be use for Rey's parentage because there were a lot of characters created in the star wars franchise like to name a few Kyle Katarn daughter or Ezra Bridger decedent, it might even be a mach up like Ezra had a daughter and she and Kyle hooked up and we got Rey. The posibilitys is endless.
Then the prophecy to bring balance to the force, there can possibility be written hundreds of books on this what it is what it means, but the true is it might not have been fulfill yet, everyone believe Anakin Skywalker was the one and he may have been if you look as it in a balance way the galaxy was full of Jedi and only three sith so he made it more balance by killing most of the Jedi.
Then if you look at Anakin and Rey, Rey is showing much more force as untrained then Anakin did before he turned so she might be the one.
Luke might have also fulfilled this prophecy by balancing Good and Evil in Episode 6.
The most important word in the Prophecy is the word Balance and than does not necessary means peace it means that there are as much good as there are evil in the galaxy.