A single sensor can simultaneously pair with multiple mobile devices.
Similarly, there's no set limit to the number of sensors you can pair with a single mobile device. I often will use a dozen or so sensors simultaneously with my one phone.
If you plan to use your sensors in conjunction with a SensorPush WiFi Gateway, same general rules apply. There's no set limit to the number of sensors you can pair with a Gateway. Also, you can have multiple Gateways on one account. They can be in the same location or they can be in separate locations.
Something else to consider about this when using a Gateway (only)... Additional mobile devices can simultaneously log into the same account provided you use the same email and password. You will not need to add the sensors, nor the gateway to these additional mobile devices devices. This is because the sensor(s) and gateway(s) are already associated with the account.
Just download the app to an additional mobile device. Open the app to the main screen (the screen with the word "Devices" at the top), and then select the settings button in the far upper left. Once in the settings screen you will see the option to login.
After you log in using the same login credentials, turn off the Bluetooth switch below in the "Configuration" section. Then return to the main screen of the app where you will see the sensor(s) and gateway(s) on that account. It can take several minutes to download all the data from the cloud.