How can a human like Yuto or Abe no Seimei live in Magano?
The fact, that Abe no Seimei is still alive in Magano, was just barely mentioned in manga, and there was no real proof for that.

Nevertheless, in ch. 17 of manga, it was shown, that exorcist may survive really long time without any supplies, based only on his divine powers. So, I suppose, the strongest exorcist in history may stay alive in Magano for really long time.

Regarding Yuto, question is slightly incorrect, since according to ch. 13,


   Yuto is no longer human anymore, he is much more like Basara being - he infected himself with Impurity, and managed to gain control over it.