Welcome and well done you for getting four animals out of a nasty situation. Perhaps the rabbit and other piggy may be next, like others have said we have a rescue locator on the page who may be able to help you liaise with the school re welfare issues and support rehoming of the final two animals. So often it seems a good idea to have class pets and it then goes wrong to the detriment of the animals.
Try re-introducing your boys slowly and on neutral territory. There will be some chasing and humping and probably squealing as they sort out their pecking order. Try looking at this thread for help. As large a cage as possible with two of everything will help. You may also not know that neutering male guinea pigs has no effect on their behaviour unlike in cats and dogs, it only stops unwanted pregnancy.
http://www.theguineapigforum.co.uk/threads/faq-introducing-and-reintroducing-guinea-pigs.38562/
If your little guys really don't like each other and can't get on then it is possible to introduce them to a new buddy. I would highly recommend getting help from an experienced rescue with this and not til the little one is over his illness. If they or one of them is neutered he could have a wifey-pig, Cross gender pairs are the most stable and a good rescue (see our locator) will help him find a lady he gets on well with. If they are un-neutered then they can be bonded with another male with the help of an experienced person. Bondings rely on good character matches and not so much on age although that is a factor. Young, excitable males are harder to bond than babies or older more sedate males. A good rescue will be able to help your guys find friends they love. I've been through the process many times and there is nothing more satisfying than a well bonded pair of piggies who love each other very much.
Good luck with you new guys. They will be back on their feet and loving life very soon with someone who cares about them. Well done. x