i don't have a cite handy, but the short answer is yes, a cpl holder may legally possess more than one pistol, including a pistol that is registered to someone else. that part is codified.
the definition of possession is most likely not defined by a law but by the courts.
I would think that a cpl holder could have a gun in a vehicle almost anywhere and claim possession as long as the non-cpl holder was not actually touching/wearing the pistol. Ie: I would be comfortable as a cpl holder transporting a pistol in a center console or glovebox even if a passenger in my vehicle did not have a cpl. however, I would not leave the passenger in the vehicle with the pistol when i got out as the person in the vehicle may be committing a felony at that point.