My wife has driven our Motorhome before, but I normally do all the driving. Honestly, I don't really see my wife or kids being able to extract me from the drivers seat if I were to become incapacitated. There isn't really enough room for them to get around me to do anything. Someone might be able to get on the ground and work the pedals while someone steers. I don't think someone needs to know how to drive to do that.
I think it is very smart going through the drill. I've done it for both car and RV. There are plenty of times when only one parent is driving the kids around. Our kids aren't old enough to drive yet, but they should know how to safely stop the car in an emergency.
-Michael
