Hi,
Yes the chemicals would probably be harmful to the snakes - even with snake mite treatments you have to make sure not to treat the animal directly and a lot of insecticides are able to infuse into the water in the waterbowl with serious consequences.
You can quarantine all new arrivals in one area - it just increases the number of animals that might require treatment if a problem is found. Most people do this but remember you have to restart the quarantine clock on ALL animals with each new arrival.
I'd suggest moving the snakes upstairs for a few days and bug bombing the basement while they were out of it.
You will want the quarantine area to be as far away as you can for new arrivals so possibly building a QT rack in an upstairs room with totally separate equipment would be a good idea? Once it is run in and tested you could then move the snakes into that during the bug treatment. Also remember to finish any work with your existing collection before going near the QT area each day.
ETA: ^^^^ he described things way better than I did.![]()