You really need to get those sick birds away from any healthy birds you have. The first rule of getting new chickens when you have existing chickens is QUARANTINE!! However, I've got to say, and I'm sorry if I sound too harsh...You should've never purchased a bird that was showing any swelling in the eye, nasal discharge or anything in the first place. It's possible that since it's been 3 weeks, all of your birds have been exposed to something nasty, especially if they have an odor with the discharge. Vicks will not treat a contagious disease. Your best bet is to cull all of the sick ones because if you treat them, they'll still remain carriers and will continue to infect any chickens you have. As far as treatment goes (if you choose to go that route) I think the best antibiotic you can give them is Tylan 50 injectable. I believe the dosage for standard chickens is 1/2 cc in the breast each day for 5 or so days. 1/4 cc for bantams.
Like I said before, I'm sorry if I sound harsh, but I'm just trying to help.