I'm going to say here and now, if we learn anything about Rey's parentage in this film, it'll be that she's not related to anyone from the previous cast. She doesn't have to be a Skywalker to have a powerful connection to the Force. As shown in Clone Wars and Rebels, Force sensitive children pop up all the time.
If anything, I think that Rey may have been the daughter of someone on a pirate crew or kidnapped by a pirate crew, or something that crashed on Jakku. They didn't have enough coin or trade to get parts to repair their ship, but Unkar Plutt would accept young Rey as a slave. The pirate crew, being a pirate crew, leaves Rey behind and goes on their merry way. If someone were hiding Rey on Jakku, why leave her with someone as vile as Unkar? Not exactly a grade A guardian, and it doesn't seem like Lor San Tekka was a Ben Kenobi secretly watching out for her figure.