Ferrets not getting along while ferretsitting

Question
My boyfriend and I own 4 wonderful ferrets. They don't have any really bad behaviors or habbets until we started ferret sitting a friends ferret. We will have her for awhole, almost 3 months and this worries be because our smallest( Flower) and the new ferret (Ned) do nothing but fight. I have an idea as to why they may be fighting and Flower is definetly the instigator but I'm not sure why I should be doing about it when the fighting accurs. Should I let them fight it out or should I separate them?

Answer
I have a tendency to let them sort it out, but it depends on the space available.  If they have a large-ish space, like a room then there are places to go to get away from each other.  If they are in a cage together, I would probably split them up occasionally to give them a break form each other.