There are three separate hydraulic actuators for each elevator. The servo valve controls have jam-tolerant mechanisms, so a jam in one servo valve control will not cause the whole system to be jammed. I'm not sure how the servo valves receive their position feedback from the elevators.
There are pitch control runs from each control wheel back to the elevator servos - left control wheel connected to left elevator servos, and right control wheel connected to right elevator servos. The two control wheels are connected via the disconnect mechanism (actuated by the PITCH DISC T-handle).
The autopilot commands to the HS trim have their source in the autopilot servo torque that is commanded. If the servo torque required exceeds some threshold for a minimum time, then the autopilot sends a command to move the HS.
Studying the maintenance manual a bit more deeply, it looks like my earlier statement that the autopilot receives elevator position feedback was probably incorrect. I don't see any such input on the spaghetti diagram for the autopilot.