I'm just starting to research Southern Italy for a potential family trip this summer. A few things about us. We visited Italy for the first time in July 2024, staying in Florence for four nights, then an agriturismo south of Siena for six nights and ending with four nights in Venice. It was glorious!
We'll have two young adult kids (24 and 22) with us and our 16 year old son. And we will need to travel in July, though I know it will be hot and likely crowded. That's just the reality of having a high schooler.
We're considering flying in and out of Rome or Naples. I've always wanted to see Pompeii and my great-grandparents emigrated from Calabria in the early 1900s so I'd like to spend some time there (though I unfortunately have no more details as to where they lived). We will have about 12 days on the ground to sightsee, and we are fine with doing a combo of train, plus renting a car if need be. (That's what we did before it Italy--train everywhere we could but we used a car in rural Tuscany.)
We like a combo of busy sightseeing days with some more relaxing days at our rental or in nearby little towns to just soak up the atmosphere.