It's a really nice thing you are doing by taking on the other boy
I personally would quarantine the new boy in a different room or at the very other end of the room if that's possible for a few weeks and he can still hear the other boys and they can get used to hearing and smelling him without it being in their faces, whilst the quarantine should show up any bugs etc the newbie may have. The problem with adolescent boys is that between the ages of about 4-10 months or so all the hormones are raging and most go through the sulky teen stage (like us!) and this is usually when bonding friendships are likely to be tested. If the new boy is kept at a reasonable distance but you can still give him lots of cuddles and attention, he should be fine until you can guage the situation with them all, perhaps wait for the teenage terrors to ease etc. Everyone has their own way of doing things like this, and others may say they do things differently, so that's just what I personallly do
Regarding the biting - piggies arn't by nature vicious creatures, but they can bite if they feel unsafe, like if they're not being held securely, of being mishandled and so on. Alternatively, if the person he bit had been handling veggies or food, the piggie may simply have mistaken the smell left on the hands as his precious veggies and thought it was a tasty snack for him!
Welcome to the forum by the way
Edited to add - there is some great behaviour info on
www.cavyspirit.com - go to the sectiion called "Social Life" on the left hand side menu. It gives tons of info about what to expect, options, behaviours etc