Your smaller tad might be a green frog. I had greenfrog tadpoles by my house last mid-summer which were still tadpoles, not even having small back legs yet. They could take longer than leos to change. If it is in fact a green frog, they can live well with leopard frogs, so that's nothing to worry about. I have a green frog in with my adult plains leo frog in a 40 gallon tank.