With NFL Travel Pass you can watch games, shows and more on 2 different devices at the same time, by using the same IP.
If you are having issues watching on two devices, please check that they are connected to the same internet source – for example, if you are watching NFL content on your TV that is running from Wi-Fi and you want to watch on your mobile phone as well, your phone needs to be running on the same Wi-Fi network, not your mobile data.  
You can see all the Game Pass content here.