Sadly, o one will be able to help you with this one. Sometimes this just happens. It's why we always advise if you have more than 1 chin, that you need more than 1 cage, just in case.
If one of your chins was sick, and has seen the vet, it's possible he has that funny smell. Give him time to get completely over it, then you can try and reintroduce them. There is a thread in the FAQs that explains different methods of introducing chins. You can give one or more of them a try, but it just ma be that they have to stay separated from here on out. If there has been true aggression, i.e., chasing, fur flying, biting - then I just wouldn't risk it at all.