Why are there double hinge lines on the rudders of the Grumman C-2?
The double hinged rudder is also a Dehavilland Canada feature on most of its larger designs like the Caribou/Buffalo/Dash 7/Dash 8, where maximum yaw power for a given surface area was a design priority (especially if there are height or other limitations that prevent you from adding more area by going up; in the C-2's case, they also added more surfaces as well to limit height, an obvious issue on a carrier, and the same reason the Constellation had 3 tails).
It improves yaw power for a given overall surface area by allowing the rudder to operate at a larger net angle before significant flow separation, by allowing the airflow to make 2 smaller changes in direction vs one larger change in direction for the same overall displacement.
It's not quite as complicated as it looks.  The trailing edge segment is effectively a giant anti-servo tab and is simply geared to the vertical fin by a push rod.  The actuation system only has to drive the forward segment.  The extra parts and complexity are in the second set of hinges and the actuating rod.  In the C-2 pics you can see the gearing rod attachments in the little blisters. On the DeHavilland Canada products, the gearing rod is hidden at the base of the rudder.