How are the 747-400 rudder pedals and tillers connected to the nose wheel?
Both steering methods work via a clutch (12) that engages only when the nose wheel is loaded. So in the air, the nose gear won't turn by either input, whether still extended, or retracted.

The pedals' input to the clutch is a pivot, and is therefore more limited, whereas the tiller's (15) interface is cables.



Now based on my understanding:


The pedals move the tiller but not the full range since the cables/clutch/pivot move in that scenario*
If the tiller is held in place, the cables that activate the hydraulic power steering actuators cannot move, and the pedals' input will simply pivot freely (clutch slip)
The tiller overrides the pedals for the same reason in 2.


For completeness, the main body gear steering starts only when the steering input is big thanks to a cool looking cam (29) that pivots the quadrant (23 around 31).



For double completeness, Terry once told me the linked steering is not on a minority of the -1/200 variants, so for those it was either company option, or disabled.



* You can watch it here. Note how the bumps on that takeoff bump the tiller as well.

Sources:


Nose gear steering – Boeing patent (most definitely the 747's judging by the approval date)
Main body gear steering – Boeing patent (definitely the 747's).