do the radios have an AFC switch on them? this would keep them centered on the station's signal instead of
the RF section passband is pretty wide on FM receivers (a couple hundred KHZ maybe), and the RF input stage probably consists of a transistor and a tank circuit (on some real cheap ones, it's just a tank circuit just before the mixer). one section of the tuning cap will be the cap on that tank circuit. if there's a second RF stage, the passband might be 100-200khz. after the mixer, you now have a 10.7Mhz IF, and most modern radios (even super cheap ones) use ceramic filters to achieve the proper passband characteristic. the selectivity comes from the 10.7Mhz crystal filter, not the RF stages