Just speculating Rey's family history, as this is a big topic following the film. I think that it is very very unlikely that Rey is the daughter of Han and Leia based on the movie. I think she is Luke's daughter, because she is very strong in the force (based on the movie) and a non-Skywalker super Jedi would be a mistake in my humble opinion. The Star Wars storyline is centered around the Skywalker family and a deviation from that would be disappointing. Rumors are that Rey's mother hid her on Jakku to protect her from the Jedi and the turmoil that follows the Skywalker family.