We have a 100 gal 2 year old community tank that we have had a pair of angels (Sunshine & Bumble)in since the beginning. They were total buddies. About 2 months ago we decided to put another pair of equal size in the tank. With in 3 or 4 days one of them died

Anyhow the other new one(Callie) has become best friends with one of the old ones(Sunshine) and alienated the other(Bumble). They pick on him and kind of shut him off when he gets near. Now there is plenty of room for all but I feel bad for him. What show we do?...........Should we get a few more?? Any Ideas??