I know you can have two drivers but are both of them allowed to be driving the robot at once
Generally the idea is that one controls the movement of the robot, as in drives it from point to point, while the other controls the mechanism(s) on it
The robots are generally more complex than a simple base. It quickly becomes difficult for a single person to drive the robot while manipulating some sort of arm device, a person just doesn’t have enough hands. Most teams will split up the responsibility of operating the robot to two people. Because both people think on their own, it becomes very important to have good communication and trust between the drivers. It would also help if they had some practice 
Of course, it might make the game a bit more challenging if FIRST actually required two people to share the actual driving: you take the left, I’ll take the right!
Yeah, often people refer to one as a driver ( the base or chassis controller) and the other is often referred to as an operator (arms, wings, grappling hooks. The works)
I agree 100%
yup, thats it