Tut sounds disapproving - perhaps it's short for Tutankhamun?
Doddie is a Scottish nickname for people named
George. Try the surname list for both of 'em.
As for Nerva, it was the name of a
Roman emperor, and as such masculine. Short for
Minerva - well, depends on how you feel about
Minnie, I suppose. Gives a nervous impression ... probably OK for the family cat if it's the sort that leaps around a lot.