Thanks for reaching out to the Google Nest Community.
You can replace any or all of them with a Nest thermostat. If you’re only going to replace one of your current thermostats with a Nest thermostat, it's recommended that you replace the one in your main living area. That way it can better tell when you’re home, learn what temperatures you prefer, and automatically help you save energy. To learn more, take a look at this link: https://bit.ly/3dkq8SS