There are already many autonomous trains operating all over the world. They have centralised control centers to monitor them, and then maintenance crews that can travel to work on any malfunctions or breakdowns.
This is already happening in Paris, London, Copenhagen, Singapore, Tokyo, and many more places. They all still have staff that move around the network to work on things not related to driving the train though.
So, I think you're right in pointing out that they still need many people constantly monitoring and working on the trains. But they don't need a driver per train any more, and they especially don't need two drivers per train.
No. There is no variance in the daily use of a given vehicle. It's not "today A-line, but tomorrow this train goes to Schenectady." An entire fleet is bought for use only on a set of particular routes.
This is already happening in Paris, London, Copenhagen, Singapore, Tokyo, and many more places. They all still have staff that move around the network to work on things not related to driving the train though.
So, I think you're right in pointing out that they still need many people constantly monitoring and working on the trains. But they don't need a driver per train any more, and they especially don't need two drivers per train.