Litter training and other baby related questions

Question
My daughter has a ferret, Kessler, that is about 5 months old, he's very healthy, happy, playful and laid back, and I love him and play with him a whole lot. Friday, she bought a baby ferret for me, because (and I quote), "So you will stop trying to steal my ferret."

But Wendel is very, very tiny. We took him to the vet immediately and he weighed 350 grams, about .8 ounce! The vet couldn't fing anything wrong with him health wise,and advised me on vitamins, food, ect, and said if he didn't start gaining weight quickly, bring him back. At first he didn't want to eat, but I got him to by dipping my fingers in his food and getting him to taste it. At first he wouldn't eat anything unless I did this, but now he's eating very well and gaining weight. Unfortunately, now he tells me he's hungry by biting my fingers. How do I get him to stop that?

And a second question. Kessler is *huge* compared to Wendel, and I have read that when introducing ferrets to one another, it's not uncommon for them to scrap a bit to show who is boss. Wendel is still being kept in quarentine, even though the vet couldn't find anything wrong, but when he is done with that, I doubt he will have caught up to Kess in size. Should I keep them separated for months till they are a closer match in size? And how will I know if I should intervene when they do meet, like what should I look for to know if things are getting too rough?

Oh, and can you hold a baby ferret too much? Should I just hold him for feeding and leave him alone the rest of the time, or can I carry him around in a fleece bag sometimes while I am moving around, working and so on?

Sorry I have so many questions, but aside from Kessler, I have never had a lot of experience with ferrets.  

Answer
That is pretty small for a male ferrets so I assume he is very young?  It is common for young ferrets to bite (just like puppies) as they teeth and as they get used to human intolerance for pain (we don't play nearly as rough as ferrets).  I wouldn't worry about the size difference - some of my females are 1/3 the size of my largest male and it makes no difference, plus the ferret interaction will be good for Wendel.  I only intervene if there is blood and screaming, most interactions seem rough to us, but quite normal for ferrets.  You can hold him and carry him around as much as he will tolerate it!