It gets hard to figure out what to do when they do not respond to the first treatment. You do need to be careful with giving them multiple medications. If the one that sneezed is getting Denegard you need to finish the treatment for the number of days it takes. If they or he is not better after the Denegard try giving them a couple of days off and then see if you should treat with corid for Cocci.
$10.50 and the cost of mailing an envelope to CAHFS at UCD will let you know if they have Coci and how to treat it. Use the Standard submission test and find the Fecal test. In the notes ask them to check for Worms and Coci.
Also, are you completely sure there is not a hidden source of mold somewhere? It can hide and kick out spores. Sneezing, bloody poo and Vent Gleet can all be caused by mold.
Hoping and Praying for the best for your flock!