Introducing new piggies is always tough, when my guinea pigs friend died I introduced him to my sister and brother in laws guinea pigs, they didn't exactly get on but we kept introducing them a little bit at a time and eventually they would sit together around a pile of grass and eat. But they were all male so keeping them together with out a distraction wasn't an option.
It is tricky putting a male in with females if they've already made their bonds, usually a male is bullied quite a lot from what I remember from our old male bramble and me and my sisters two females, but he wasn't neutured so it was more they weren't interested in what he was interested in.
I'm surprised that it's Tufty that took the first bite, it might just be he needs some time to get use to them, just let them meet on regular but short occasions and keep a close eye on them, it could just be they're not compatible but it's always worth trying, a lonely guinea pig is a sad sight. But you need to make sure no real damage is done too.
I'd suggest, a BIG handful of good edible grass or other favourite food. make sure they're positioned an equal spacing apart and not touching eachother, from what I've seen guinea pigs don't like to be close together or touched by those they don't know very well and thats when it can get nasty.
Food can be the keeper of the peace! It doesn't last for long but it'll give them a bit of social interaction and you never know it might build some bridges, don't get into a false sense of security though just because they're peaceful ish when theres enough food to go around doesn't mean they'll stay that way, so always keep a close eye on them and watch out for any movements toward a fight.
On the other hand if they're very protective over their food they might fight more with favourite food in the pen with them, just make sure theres LOTS of it, enough for all of them to be spaced apart a bit but facing eachother at least. It might not work at all but I think it's probably worth a try.