Please don't use flea collars! They are not safe for your kitties. You might want to go to your vet and ask them if they have a spray that is safe for you and your cats. But like previously mentioned, doing something before you move in is a great first step! You can also get a few months of flea treatment from your vet and make sure you use it on your kitties for the first couple of months you live there, like Advantage or Revolution!