Georgia

The combo of puffing up and beaks open/panting is just working to regulate temperature as mblan13 commented.

Another possibility is they have the fungal tongue infection caused by feeding at dirty feeders. Are they tilting their head back and flicking their tongues?

The head is tilted back but I don't see the tongue flicking. We scrub the feeder and change the food every 2 days so unless they are feeding somewhere nearby as well I don't think that is issue.

Sorry, I did not intend to make it sound as if I thought your feeders were dirty. But they do feed in multiple locations, and your neighbors may not have always been as diligent. I've had several sick birds show up at my feeders over the years, and it is difficult to watch, knowing there is nothing that can be done for them.

Do these sick birds die from said fungal infections caused by dirty feeders?

Candidiasis is usually fatal, as I believe often is salmonellosis. There are at least a couple of other diseases that hummingbirds can pick up from dirty feeders that I believe have lower rates, but I don't recall the estimated mortality rates for those off hand.