You normally just introduce ferrets like you would any other animal, with supervision in a neutral space. Since the ferrets don't have free roam of the house (one day I will have a house that the ferrets will have an entire room to themselves) any space outside their cage is considered neutral space to them. So we just introduced Seek to the group during play time. Once the ferrets roll around a bit and my group lets him know where he stands, then they get along great. Their first introduction went really well and we moved him into their cage last night. When I went to check in on them this morning, they were all cuddled up together.
Normally I QT any animal that comes into this house. QT is normally about 2 weeks-month depending on where ther ferret came from. With Seek, I made an exception. He came from a friend who is very neat and tidy and always keeps her animals incredibly clean. He's showing promise with switching to a raw diet too, so I've got my fingers crossed. When we go grocery shopping and pick up more meat for the kids, I'm going to get some chicken baby food for him to try.
Ferrets do form a pecking order. Twitch is the boss even though she is the 2nd smallest ferret in the group. She was the first ferret and therefore, she is boss. Or so she thinks. Kale is trying to win her spot though. So far I don't think he has succeeded. Ferrets fight all the time. Its the way they communicate, play, and make decisions. Its very rare for a ferret fight to end in blood.