If both of them are juveniles ocellaris clowns, then add them together. Before I continue, yeah MOVE the yellow tail.
Anyway, many people believe that ocellaris are better in pairs. If you introduce both of them when they were young, the chances of them to be paired is pretty high. Go ahead, and try to do that. You will have a cute couple in your tank.
However, if you don't then one will establish its territory and it will be hard for you to introduce another same-species fish to your tank. One of them will be territorial.
stupid naso