We could certainly use both of them. Calathes in particular is underutilized and may go back to Greece if he doesn't get a decent shot somewhere soon. It would be too bad, he's a good PG with size and a good defender.
The player I would really like on the Celtics though is Kostas Papanikolaou. He's the best of the three, and not being used at all in Houston since they got Josh Smith and since Terrence Jones returned.