Different logins/users can share/be paired with the same Cooksy. A Cooksy can be used by any login as long as it is on the same Wi-Fi network as the Cooksy.
Once a Cooksy had been configured on a network, showing the solid green light while on, a new user can connect to it. You can pair to it in two ways. First is selecting "Setup Wizard" within the Cooksy app and choosing "Use an existing sensor". The second way is to open "Nearby Sensors" from settings and select the sensor that is found on the same Wi-Fi network.