jet set lady, all good questions and valid ones. It is probable that if both pilots are incapacitated then further damage to the airframe and controls is likely. The chance of shutting an engine down will be partly dependant on the make and model of aircraft. Many aircraft these days have electronic control of the engine start/stop systems in the flight deck. All you would need to effect a shut down is a complete electrical circuit between the master switch, the FADEC and the engine fuel valves. that may be more likely that older types where controls were cable actuated.
If engines were running and CC had to initiate an evac with incapacitated FC, do any of your company procedures preclude use of exits forward of the wing?