Thanks for all the input. I just finished the treatment on the two of them; today their legs look better, the puffiness has gone down, and I treated my coop with diatomaceous earth. I hope that will work.
I suspect that two of my Barred Rocks have leg mites, but they are only twelve weeks old. I was under the impression that this was something that affected mostly older birds. Their legs have had some scabs on them. A few times I have also noticed some swelling with exudate underneath the scales...