I did check yesterday, no neutrals in any of the 4 boxes
In older construction (that is just about everything built until rather recently)the lighting circuit feed wire went around the structure
from room to room to room *at the light fixture*.
From there a "switch(ing) leg" was run to the switch.
For three ways additional wire is then run to the other 3way switch
(and/or 4way switches used. How all this gets done will vary.
Some of that variation can get very creative.
But NONE of these methods will put the neutral wire into the circuit...
(the same neutral wire that the sensor device requires to operate).
See diagram at bottom for one commonly used method.
Hopefully your church has always been a commercial building and the codes there required the electricians to use metal conduit.
That will make sorting this out merely tedious rather than a major PITA.
Your mission Mr Phelps, should you choose to accept it, is to find out what is installed there, what type of wiring methods were used and how the circuits have been run.