Two thoughts.

The first is that one of logic.

The problem with most of these fan theories about Rey’s identity is that they involve the same two fallacious arguments:

A. That she must necessarily be related to someone else that we’ve met in the films; and

B. That we can deduce her identity based on the information that we have.

Neither of those statements is true.

The truth is that Rey could be just like Han Solo when we met him. Or Chewbacca. Or Obi-Wan. That is, completely unrelated to any other characters.

Secondly, the value of a theory is based on how many assumptions it has to make in order to explain what it’s explaining. In other words, a theory that has to assume most of what it’s explaining isn’t a good theory.

The notion that Rey is Obi-Wan’s granddaughter assumes that A.) Obi-Wan had a child of his own that we know nothing about and that B.) that child grew up to create a child of his/her own.

Given that nothing in the canon remotely hints at such a thing, these are two pretty big assumptions.

As far as Alec Guiness’ and Ewan MacGregor’s voices appearing in the vision….well, so did Yoda. Should we assume, then, that Rey is Yoda’s offspring?

Of course not. Instead, we could argue that Obi-Wan’s voice appears for the same reason that Yoda’s voice appears: she’s a fledgling Jedi who’s becoming aware of her powers and these two old Masters are speaking to her through the vision to help her start on the path. No blood-relation required.

One other thought:

The filmmakers have already used the “surprise parentage” plot device once. To do it again would — in my opinion — be lazy writing and a real disappointment.

I’m perfectly satisfied with Rey having ZERO relation to any of the other characters and simply being what she appears to be: a brand new character who’s capable, intelligent and on her path to becoming a Jedi.