Did you properly introduce all your rats?
Rats can be territorial, and they need time to get acquainted to new buddies.
Already 2 rats that have been living together since birth are bound to fight a little to establish who's boss. When you introduce other rats they have never seen before, even if it's only 2 days later, you need to have the rats seperated and let them meet in neutral territory that smells neither like the old or the new rats, so they meet on equal grounds, and keep them in seperate cages until they get along on neutral territory without fighting, then clean the cage you want them all to live together thoroughly so it doesn't smell too much, and make sure they get along in the cage.
As long as there's no blood, it's not bad. They will "fight" until the places in their little herd is set and the boss has what she wants and can be dominant.
If you see there's blood, or you think the ones without hair are too scared, seperate them like you did, and introduce them as though they don't know each other on neutral grounds. Give them all treats at the same time to keep them busy and such. Just having the cages close together without touching so they can't bite through the bars will help them get used to each other's scents.
hope this helps a little, i'm sure others will be able to advise you even better