This is all excellent info, that I need to re-read now that the trip is starting to come together (translated: BIL finally got around to asking about allowable expenses with his daughters on the trip).
Basic outline: Sorrento (2d), then Capri (2d), then Naples (3d), then Sicily (4-5d), then re-positioning flight to Naples or Milan the night before flying home. 15d total including the international flights for wife + me; BIL + nieces leave after 1 week.
We will visit Pompeii and Herculaneum from Sorrento ... thankfully, since that affords us more time in Sicily.
We still need to figure out where in Sicily. Any thoughts? We're basically down to: Siracusa with day trip to Noto; or Palermo with day trips to Monreale Cathedral and Cefalu.
I'm curious about Sicilia too. That's on the list.