Without seeing the teeth and their xrays it is hard to make a judgment call here. All I can say, if both dentists say to fill a particular cavity I would do it asap. As for the teeth that you're not sure about, go to a third dentist and see what they say. If that dentist says that those cavities need filling then do it asap also. Good luck.
Caries has active and inactive state. The one who diagnosed minimal caries was most likely correct. It's really a piece of cake to detect or diagnose caries if radiographic image is available for licensed dentists. Keep in mind dentistry is a business. Your descriptions appear you have sound dentition, no need to worry. If in doubt, go to dental school, I believe dental schools are academic oriented, there is no commercial interest involved.