New ferret attacking our other two/ripping one's hair out...help!!

Last Sunday my husband and I adopted a new ferret, a boy (we already have two girls). We started off with one female originally and adopted a second female from a shelter; they got along quickly -- no physical fighting at all, although our first female was stressed out/had diarrhea for the first week. I knew we'd gotten lucky before, and was expecting things to be harder this time around. We do not keep the new boy with the girls, although we do let them have play time which is occasionally unsupervised. They have all slept together on their own, but eventually the boy always grabs one of the girls by their neck, pins them down while they screech. Our one tiny girl has given in and he doesn't bother her too much, but he is relentless with our more dominant female -- biting her daily, ripping out her hair. She does retaliate, though the boy usually wins...sometimes he will walk away when she fights back though. I've read to just let them fight it out and establish a pecking order...which we've been trying to do. But the girl who's having her hair bitten out is stressed and I hate seeing her with little cuts on her back and missing hair. Basically I'm looking for advice or your own experiences bringing a new ferret into your home.