I remember in a previous thread someone pointed out that it was Jenova taking on the form of Seph that killed Aeris. Because, like said, he never leaves the crater, because throughout the course of the game, and apparently from a point 5 years prior to the game, he's been frozen in the northern crater. Close to the end of the game, you go up there and free him yourself. Its not him physically doing any of it. And the clones, as stated in yet another thread/argument, are merely referred to in that way because of similarities in uh genetics I suppose, body content. Mako treatment and Jenova cells and whatnot. They weren't cloned from Seph DNA like in some science fiction movie. So any resemblance to him would have to be Jenova taking his form. Because the "clones" running around look like who they are, they dont look like Seph any more than Cloud does.