Two Red XIII questions (minor spoilers)

[Big D]

If he was marked as "13" does that mean that others of his species where captured too? I doubt it's the same number marking as the Sephiroth clones as they are all humans.

I doubt it because the only three of his species we're ever told about is Red, his mother and his father. I was under the impression during Hojo's tenure as Head of the Science Department, Red was the sole survivor of his species as we never see or are told of any others. Presumably if Hojo had captured more of Red's species then Red or Bugenhagen would've known about it since Cosmo Canyon seems to be their homeland.

Hojo seems to believe Nanaki is the last of his kind, too.
Obviously this is later proven wrong, but Nanaki's kind are definitely sparse.