I would take them to the vet! I hope your little ones feel better soon!
As for molting/preening? I see it so frequently that it doesn't look out of place to me. I have no idea what my humidity is. I sense my place fairly dry, but can get the humidity from my windows outside sometimes. I live in a wet climate. Get the rain here a lot. Right now they are looking really fine. No nasal discharging is coming from my birds. No rapid breathing. They get their rapid breathing after they fly around a lot. But not when they are relaxed. I don't hear any clicking. My new bird I hear some rasping in the throat at times. (I don't have that much money for the Veterinarians. Only if I knew they would really do me some help, but by experience they have only been wasting my money in the past. I need to be very conservative with my financial situation. I live on a budget that makes me run empty on my money monthly.)Sorry to hear of your mother passing away Michael...:hug:
Are your bird's molting/preening a lot ? How about the humidity level in your home, is it very dry ? Do you see any nasal discharge, see any rapid breathing, or hear any clicking sounds in their breathing ? It certainly wouldn't be a bad idea to get them in to the avian vet, definitely should if any of those other sign's are present.