Chickens do not get colds. They get contagious respiratory diseases. An individual might have a dust allergy or minor sniffle, but multiple birds with symptoms almost always means contagious respiratory disease, usually Mycoplasma G. or S.
You should have your birds blood tested. It's the best way to determine what exact disease you are working with. You should not under any circumstances sell or give away any birds from your flock for the foreseeable future, even birds who seem healthy - almost all birds exposed to these diseases will contract them and become infectious "carriers", even if they never show outward symptoms.
There is no cure for Myco or any of the other common diseases but there are treatments for the symptoms. I'm sorry but there are no truly effective home remedies. For Myco, Oxytetracycline (brand name Duramycin or Terramycin) is the most common antibiotic used but it's relatively mild and won't relieve severe symptoms. Tylan is another option and it's quite a bit stronger. Denagard is the most effective but it is pricy and must be ordered online. Considering that you aren't yet sure what you're dealing with, Oxytetracycline is probably the best choice, since it's the most broad-spectrum.
This is a very hard process to go through, believe me, I understand. But as someone who has kept a Myco positive flock for over three years now, the most important thing you can do right now is get your birds blood tested to confirm what you're dealing with. Many of the common respiratory diseases will present with identical symptoms but not all can be treated with the same medications.
