Sorry for my late answer.
Are you sure the DEF names you use for the pedestrians correspond to actual Solid
nodes that include the bounding objects of the pedestrians? If it is the case and the problem persists, please open a support ticket and upload a simple simulation that demonstrates the problem (with a single pedestrian and a physics plugin).
It is not directly possible to determine from a list of geoms (derived from a space) which are the DEF names corresponding to each geom. Instead, you should rely on the dGeomGetPosition() and gGeomGetRotation() functions to determine the geoms offsets with respect to the space and deduce the corresponding Webots object.