Thanks everyone...
The coop ceiling is insulated with old pink fiberglass stuff mixed with mouse poop, sheeted with thick plastic - no idea how old that crap is. The plastic isn't wet but there is frost on the windows inside the coop.
The windows are old, big hinged affairs that are sealed shut for the winter, you can't crack them open as they let in big cold drafts.
I've explored options for this place for so long, my head is exploding.
If we weren't selling this place next summer, things would be different, we would have invested in renovating everything.
I do agree that the germs are probably being circulated around the flock now and the only way out of the mess is to get a good air exchange system in place ASAP. I'll start adding poly-vi-sol to their drinking water tomorrow. The flock gets excellent food, on top of their high-protein crumble mix I cook for them like a fiend. Lots of fresh fruit, veggies, grains, meats, seeds, grit, DE, everything.
I just want the house bird-free, the smell is terrible and DH is being patient but has limits...
Plus we're showing the house as of mid-January for the sale and CAN'T have birds blocking the main bathroom. Everyone needs to be healthy and back into that coop.
Oh well. Gotta pick up my bootstraps now, the flock is counting on me, one two freeeeezing!