If you do decide to take the cats outside, do so on a secure halter and leash. Unfamiliar water often causes diarrhea. When transporting the cats, make sure they are in a secure crate or cage. Cats can travel together in a single crate or separately. If the cats aren't accustomed to car travel, don't be surprised if they spend most of the journey yowling.
Cats also become carsick VERY easily.
Be SURE your cat has adequate identification. Make sure it has a collar with an ID tag that clearly identifies the cat's home. Having microchip ID is also a good idea. But ALSO include a temporary ID that identifies where the cat is staying while you are in the cabin. If someone else comes ot the cabin to clean, make sure this person knows about the cats and the rules about not leaving doors and windows open.