I initially started with a sorority of 5 in a 10 Gal. tank. We lost two of the females to popeye... since I saw them teaming up, I just added one back to the group and after the first hour of sniffing each other out. They are now all fine together.
The smallest female (blue CT, Jolly Roger) seems to be the most aggressive but she usually gets round up by another one (read CT, Blackbeard) who looks like the leader.
I was advised not to put more than 5 in a 10 Gal tank.
Make use to have hiding spaces in the tank and try to spread them out when you are feeding them. Our four always huddle together when I come with the food and I am using my finger outside the tank to get at least two of them to the other front corner. They are really trainable...