Maybe a small school of a type of tetra with 3 cory's?
You need to have at least 5 neon tetras in a tank. They are much happier with higher numbers. How about put the neons in the new tank, add at least 3 more and the 3 cories? And then add some tank mates for the fish in your other tank?
Most, but not all, fish would prefer to not be the only one of their kind in a tank.