Does anyone have a geological or topographical map of that area of the continent?
The map will show you that the Mediterranean is a tectonic plate margin with the inevitable volcanos, huge mountain ranges rift areas and a complicated geology. It’s most likely that Naples was built on a margin plume, hot spot as well. Two huge volcanos sharing a common magma pool is scary. However, there have been numerous small eruptions which bled off some of the potential. A super eruption is inevitable in the long run but not guaranteed in the near turm.