Kylo Ren and Rey are siblings? Possibilities?
They could try to say so if they wanted but it would make more sense if Rey is Lukes daughter. Remember how in one of the trailers Luke is talking about how the Force runs in his family? Vader, him, Leia and he mentions "you have it too." That seems an awful big tip off to me about it. Not to mention the whole lightsaber thing.
That and it could add why Luke went into hiding, not only because his Jedi were wiped out but he lost his child in the process who turns out to be Rey.
Likely why she was left on Jakku, to keep her safe from those that killed the others and were surely looking for Luke and those closest to him.