While it’s certainly not recommended, a cat could live in one room as long as it’s large enough to have all they need as food and water with a separate space for litterbox.
At least a 12′ by 12′ room, but it’s more important to make sure that our feline friends get the love, attention, and stimulation they need to be healthy.
The biggest difference between one and two cats is the issue of territory and both cats will need the opportunity to establish a specific area that’s their own.