put it in its own tank, throw in something for fin rot, and then I would add some melafix and stress coat (I always say that, but it worked verry well for me)
For a complete recovery I'd say isolate the fish and treat it, feed it good food. In a seperate (hospital) tank would be best so you can raise the temperature a bit and add what you need to to the tank.
Moving them might be stressful...but I think in the end they'll make a more complete recovery not having to compete for food or dealing with the other fish etc.