They're probably just working the pecking order out, they sound cute (well all mice sound cute, don't they?)
I've found the female mice to be surprisingly territorial. Mine don't fight, although they occasionally chase each other around in little spurts for like 5 seconds at a time. They then curl up together in a little ball in their nest box, so I know it can't be that bad :)
My Daisy mouse is definitely the Queen Mouse, and I did see her humping on one of the others more than once. When I've introduced new ones, it's always been necessary to remove Daisy and let the new one aclimate to the other girls, and then put Miss Thing back in there to straighten everyone out. She tends to hassle the new one for a few days, but has so far learned to love everybody. She's just a little bossy, that's all.
Interestingly, Daisy is by far the friendlyest, has never shown any fear of us, and will come running and climb up onto your hand. She really seems to like being handled and is the only one that doesn't poop all over me when I hold her. I'll put a picture of her below, good luck with your mice!
