+1 To getting them all fixed if they haven't been already. They'll mellow out about being with new ferrets a lot after that. I've had some experiences with introducing new ferrets, and what I've learned is that you sometimes have to let them "beat on each other" to establish some kind of pecking order. They've got a really thick hide and even though it looks really bad to us, it isn't that bad to them. I break things up if one of them starts to squeal, and DEFINITELY if one of them manages to draw blood, though it hasn't ever happened between mine.

Another thing you could try is keeping them in the same room, and if they have little cloth beds or something in their cages, swap beds so they get used to sleeping with the scent of the new ferrets. Then start letting them out to play around the same time, and then you can try introducing them into the same cage (if that's your goal).