He discusses Aulus's role as if he weren't playing it himself. So, if he's not Aulus, he can only be Piona among the peaceful characters.
But then, the negative role must be either Arandor or Mornie. And as I understand it, both Florias gave Mornie a good reputation, so he can't be Necoran.
So, what are the possible negative roles in your version, Medj? List them out...