P.G.
Talk to your vet about this, and also google for info. You'll get a whole bunch of info. Probably one of the most important things is them being comfortable during transport. And you don't want them underfoot and freaking out while things are being packed out of/put into the new home. They need to be somewhere undisturbed (Kitty in bathroom, dog in yard?) while the craziness happens - at both locations.
Good luck!