If they are the reptile experts they are promoting themselves to be, I'm a bit amazed they told you to house them together quite honestly.

Just make very sure they aren't leading you on trying to get to the end of that guarantee (not saying they are, but still it's not unheard of). If there is a time concern for test results, insist on the guarantee being extended or get your money back immediately.

Whatever you do end up doing I'd be quarantining those snakes in seperate rooms until you are absolutely sure everyone's healthy and then keep them housed seperately. You don't need to spend a fortune on a fancy setup. BP's do very well in reasonably priced plastic tub housing. Even if you prefer to do a glass tank down the road, plastic is best for QT as far as being easy to sterlize and easy on the wallet.