Chatterbox needs a cage that is a minimum of 18"x18"x18" and bigger is preferable, no matter how big Chatterbox is at this time. I always suggest a minimum of 30"x18"x18" for a single budgie.
I recommend you move Chatterbox's cage into a different room for now. Having that cage right next to the cage the others are in is definitely going to frustrate him. Julia's suggestion of playing the radio and/or TV for him is spot-on.