get worried and usually quarantine them immediately if not better in a week, they get whacked. Try some broad spectrum antibiotics on them, any of the "mycins" or tetracycline's help. If it's just a cold. I worry about MG with it cause if it's that ( CRD) it is not curable, will spread like wild fire and will be carried by all birds who get it. Most will recover from it, but by being carriers of it, they will spread it to all new comers and it will pop back up in them too later on in times of stress.
Dont freak out just yet though. It is common this time of year for birds to get symptoms like this. Dose them up good and see what happens, but if they dont get better soon, well... depends on how big a gambler you are. Watch for eye swelling. MG will often clog the sinus walls and cause them to swell. Looks like the eye is swelling but it's actually the tissue under the eye. IF you see that, 99% shot it's MG....CULL THEM!!
Hope it's not and is just a winter cold.