Just a heads up, sometimes snakes whistle quite bad in shed, due to the skin it their nose getting loose. Its like us trying to breath out of our nose with a stuffy nose.
The other snakes may be fine, just make sure you sanitize very well.
I recommend to bump up his heat though, and if he is open mouth breathing i would remove the water bowl for the night, then re-evaluate tomorrow.
It sounds like a respiratory infection, it is very easy to prevent, and most snake keepers will experience it at one time or another. Its pretty tough because he is in shed to keep the humidity down though...I hope someone else will chime in with a idea on that one... haha
Just watch the snakes, and take him to the vet. everything should be a-ok.
-Theo