Update...
I haven't separated anyone, but the plastic wrap is working well to hold in some extra humidity. And that extra humidity is working very well.
Inchworm and Sweetpea have gone from good eaters to downright aggressive, striking at the food, me, each other and anything else that moves! I've had to break up two food fights in as many days.
And Checkers, lo and behold, ate three pieces of trout today, not nearly as much as his siblings, but twice what he's been eating lately. To top it off, instead of running into hiding immediately after his food, he's been lounging up on the branches for the last few hours.
I'm really hoping that the winter dryness was a big part of his problem, and that things turn around now.