I would suggest handling controls is acting as a member of flight crew, would you not ?
This is where different country's have different views.
What defines flight crew required is in the aircraft speks. Mostly these days its just pilots but in the old days it was Navigator, radio operator, flight engineer and of course the pilots.
Of course for a light aircraft it just one pilot the PIC.
There is nothing to state that the flight crew needs to be the one handling the controls. Just that they have to be at a functional set during flight.
You can't for example like some have been done doing, be PIC in the rear seat of a four seater.