About to get a new snake from a highly reputable breeder....I am aiming for 75 day quarantine...in the same room but I have bought a negative air pressure "glove" box like you see in science labs and medical shows.
Lots and lots and lots of things are airborne....some of which can only survive outside of the body for mere seconds (HIV)...other nasties can survive for hours, and days like influenza, and many bacteria (some even years and decades...nasty little endospore forming bacteria)
And if you absolutely cannot keep them in separate rooms at least follow the order of new snakes last for anything you do. The further apart they are the better...and make sure w/e tools/equipment you use for quarantine stays for quarantine.
For me personally anything going into the negative pressure box aint ever coming out with the exception of the new animal once quarantine is completed. Once QT is complete the entire box and everything in it is getting sterilized.