Ferret bites cat bites ferret

Question
I have 2 ferrets and 2 cats. My older cat (12 yrs) doesn't care about the ferrets one way or the other. She lays up high and just watches them with "apparent" disinterest.

Now, my kitten (well, he's about 9 months now, wow.. ), and my ferrets, get rough with each other. The male ferret doesn't seem to get hurt, but my kitten keeps wrapping his front paws around the ferret to hold him in place and then bites the crap out of his neck. Lego just lets him do this and when Kira (the kitten) lets go, Lego just waddles off... not urgently, but just like he wants to be left alone.

Now the female ferret is a biter. (and a kisser. heh) But she'll bite human toes and heels and even my lip. She was kissing and then decided to chomp. I bopped her on the nose and put her in the cage and said NO in a stern voice. I dunno if that does any good with ferrets... they're very tenacious. *giggle* But she really really seems to be aggressive toward cats. My older cat stays out of the way so no big deal there. But my kitten and her will try to be the first to get the upper hand and bite the other. But Sage (the female ferret) actually HURTS the cat. Took him a minute or two to realize she wasn't playing and he yelped and ran off.

Now I've been keeping the ferrets and kitten separated. Obviously the thing Sage is doing is bad and I'm gonna try to figure out how to curtail it. I keep her from biting my toes/feet by just moving my feet around whenever I feel that cute little nose on my feet. I think she's trying to say "PAY ATTENTION TO ME!", so I move my feet and then give her attention. But she has bit my 20-yr-old son a few times.

But the biting thing between my ferrets and kitten, not talking about Sage with the hurtful bites (which she has found works really well on the back of the cat's back legs/feet/ankles), the neck biting... they seem to be biting VERY hard. And sometimes one will lay there (especially the kitten) and let the other one just bite the snot out of him/her for a while, then decide it's their turn. I've been afraid they're gonna try to kill each other.

Is this behavior normal? Should I keep them separated (even if I get the girl to stop her painful biting)? Or is this something I should let them work through, with close supervision obviously, until they work it out?

Answer
While it seems a bit excessive, I would go ahead and let them play with each other.  Both seem to respond appropriately to the rough-ness in the other but yelping and running away.  That being said, I would certainly supervise very closely to make sure it doesn't get our of hand.