Well, bad news: I went to check on the little guys and feed them, and I immediately noticed that the one with the most ich was spiraling and defecating now instead of swimming normally or even on its side. I'm wondering if it was going into a death spiral of sorts, but I'll find out soon...
The other mono with ich seems to be improving now; the ich appears to be receding now and it's swimming better now. The final healthy fish is doing well, so hopefully it will stay that way. Both of these fish are still eating well. They were both hanging out on top of the under-gravel filter outlet next to the heater when I checked on them instead of hiding in the fake plants; is this normal or could it be related their health?
I'm not sure what the deal is with these fish. I've never had this much trouble with fish before, but I want to get these guys back to being in good health.