I agree that it's Infectious Coryza, the foul odor is a dead giveaway. Here's a link to poultry diseases, scroll down and read about Infectious Coryza. There are treatments for the infected birds such as sulmet in conjunction with tylan 50 injectable. Recovered birds will remain carriers and will spread the disease as mentioned. I recommend that you cull unless you're prepared to spend $$$ treating them forever with medications never being able to eat the eggs due to withdrawal periods. Also you'll have to practice strict biosecurity measures.I am so sorry this is happening to you. Give Dawg53 a shout. PM him for suggestions if you are too mindboggled to think. He will probably suggest you cull everyone. He will also give you the best advice on how to treat. He is very knowledgeable and I would follow his treatment plan. This may be the way to go. You can write a PM and wait for the answer to come to you. It is so very stressful when faced with these kinds of problems.
http://edis.ifas.ufl.edu/ps044