Infected flock: contemplating culling

[2 Acres]

I'm sorry you're going through this.
One of the signs that a bird has Coryza is a foul odor around the head area. Just for your information, CRD aka Chronic Respiratory Disease is Mycoplasma Gallisepticum (MG.)
It's entirely possible that your birds can have both diseases at the same time.

I believe you've read enough literature on both diseases and I also believe that you know that you must cull your flock. Otherwise you'll be treating sick birds for the rest of their lives.
Antibiotics are a temporary fix and only mask symptoms and will not cure the diseases. They are temporary due to the fact both diseases will eventually build resistance and then a more powerful antibiotic will be needed. As always there are egg withdrawal periods, IF the sick birds lay eggs at all.

You already know that stress brings out symptoms. It's not hard for chickens to get easily stressed. I highly recommend that you make the tough decision to cull your flock and bury them deep far away from the coops/pens or incinerate them.
Then thoroughly sanitize coops, nest boxes, roosts including getting rid of bedding or burning it.
Then wait until next spring to repopulate with new birds, preferably purchasing chicks from a reputable hatchery or a feed store. Dont be afraid to ask the feed store personnel what hatchery the chicks came from, and not from the local farmer down the road.
I wish you the best and good luck.