The ringer is inside the phone and is set off by an electrical impulse sent from the phone company. We used to refer to it as the "ringer equivalent". Some old Western Electric phones had ringer equivalents of 5.0 (very strong), some of the free giveaway phones that came out had RE's of 0.0, meaning no audible ring.
I'm not sure what it is causing your problem danger. Perhaps it is the ringer equivalents, probably exacerbated by the quality of the bases sending signals to the handsets.