As far as Leo understands it, there is only one Leo. The other is always just outside of his field of view and note that Jas can see only one while Vinny can only see the other. All looks normal to everyone else and nobody ever sees the two at once, thus retaining their finely balanced detente. Leo has a natural aversion to mirrors which could dispel the delicate balance but nobody thinks anything about it because of his naturalistic upbringing. Plus he assumes the other Leo is his funny reflection in clean glass. And so it is. The Junimos have tried to tell Rasmodius about the duality of Leo but his stubborn inability to understand Junimosh is why they love telling him. Because laughter is universal and he can discern a Junimo snicker a mile away.
However one of the Leo does suspect there's another because dangit someone's always using up his vacation time.