The kittens got removed from behind the washer this evening and relocated to their carrier so that I could do laundry without freaking them out. They weren't too happy about that, but the operation was successful. While they were in there, I covered the gap behind the washer so that they couldn't spend all their time back there.
Oh, and I changed the sensitivity on the webcam.
Much to my surprise, they came out and started playing within a minute of my leaving the room. Sweet! They're still pretty freaked out about that big pink-haired monster coming around, but they do OK once I have them in my hands.