Thank you all. I was able to get him to the vet. today and she was super helpful. Obviously, it's bumblefoot.
I feel HORRID for not noticing this sooner, and the thought that they've all been suffering makes me sick to my stomach. I've only had them for a few months and they likely had it when I got them but I should have caught it long before it got this bad.
The good news is that there is no osteomyelitis and no joint involvement, so we're going to take him back on Thursday to be debrided under anesthesia. My wife is a nurse practitioner and a wound care specialist, so she feels confident that we can manage the other two at home, and that with the help of antibiotics we can get Roy healed once the wounds are clean. As I type this he is outside chasing the girls around the yard and bossing everyone around so I take a tiny sliver of comfort in that, but I feel horrible.
Thank you for helping to confirm that my fears were correct.