If you are using a tablet that is assigned to a specific driver I would tend to think that you each would have to use your assigned device.
We followed @Boattlebot's advice, and were able to log both of us on the same device. It took a little trial and error, but we figured it out. We were able to log in, and I'm currently showing in sleeper berth.
On my Qualcomm Omnitracs go to the main page and onl the upper right is the LOGIN button onscreen. Pressing that you each login.
always double check that you actually switched drivers. It's easy to screw up and somehow both people are on duty. (1 driving)
You have to be on duty to switch your co-driver to active driver. You can get around this by logging out and then logging back in as the co-driver. This is useful if you performed a post trip but forgot to switch, or if you already made the switch but want to become the active driver again. You don't want to interrupt someone's break to go on duty for 15 seconds just so you can switch drivers. If the co-driver is off duty and the vehicle goes to "in motion", it may end up starting their 14 hour clock at that point. It doesn't matter if you've been off for 102 hours prior to that. You also can't enter sleeper berth unless the vehicle has had a pretrip performed on it. If the co-driver is ever prevented from entering sleeper berth but you have to move, just log them out of the device until they're ready to drive. Don't move the truck if it hasn't had a pretrip performed on it. Our device will flip out and make noises, and become inoperable. We end up having to shut the phone off and rebooting it in order to interact with the app. These bugs or glitches rarely happen, but if they do at least you'll have an idea of how to handle it. Also, if you leave your device screen on basically 24/7, I would advice against it. Our phone has a faint line burnt into the screen from where the "in motion" tab turns bright white. If you've got the screen off, you should still get audible warnings.