They could use the GPS in the phones and downloaded maps if there's no cell service.If possible they should use as few tables as possible. The conductor, and assistant conductor would need to see out the windows to do their job safely. They have to know the precise location of the train.
They could sit at an empty coach or business class seat and work there, like I used to see crew do on the Northeast Regional. They could also use an empty sleeper compartment to do whatever paperwork needs to get done. Finally, they could use the obstructed-view cafe table seats, if they need to, but they shouldn't need to take up more than one booth.
Has anybody ever brought this issue to the attention of Amtrak management? Has there been any response? Has RPA weighed in on this? This seems like an issue that could be resolved without any complicated acts of Congress or major management changes. Seems to me that the easiest thing is to always hold 2 coach seats in the reservation system, and reserve them for crew use.