But ... they would have grown up, yes? And known who they were. And the sister knew. I mean, there'd be some evidence of them somewhere, some time when they appeared in the historical record in some way, even if only to renounce any claim on the throne.

I am by no means an expert in the story, but it seems they vanished. And with royals back then (well, anyone, really), that tends to mean dead. And I can't see how it can be of natural causes - so, assassination.

I do wonder if, as with Richard himself, technology and time will reveal what actually happened in my lifetime.