What type of cory is the other one? Try to gte a cory taht's of the same species as one of the other two. At least that way one of them'll be somehwat more social.
If your panda doesn't want to play with your other cory, it could be because of the difference in size, either now, or the size they will be when mature. If you have an albino C.aeneus it will be quite a bit bigger than a panda. Sometimes they school together, sometimes they don't.
This link has a picture of the albino cory. Is this what your other cory is?
When you say "baby," are you talking about the angelfish or the cory? If it's the angelfish, you are probably going to move that, right? I would not suggets having even a baby in anything under a 30. It needs room to grow and to keep aggression down.
Your sig says you have a "baby angelfish" called Ange. Are you planning on moving the angel any time soon?
Sorry I don't mean to go off topic but tempestuousfury's post highlighted it. Angels need much bigger sized tanks that that. Nothing less than 30galls and 18" high IMO.
Now for more on topiv, a reason that the cories are not staying together could be as Inch mentioned the difference in size. Cories often only school with cories a similar size to themselves.
I think I remember you posting about a little tiny albino cory. If so, I think he'd love to have another one to hang out with. It might do him a lot of good.
so which is it? sorry but ur contradicting urself, and its not an albino cory, its the regular 1 of the albino kind. i went 2 get one but the store didnt have any so i got 2 gouramis instead. i think now its enough fish.