Fantastic post Perche, thanks for the advise. And it's a party of 3, but close enough.
And we won't be doing any beach stuff anyways. I guess Ravello was just for sightseeing anyhow and dinner - but I suppose since you say most places will be closed we'll rethink that. Reason we were considering doing Postiano/ravello/amalfi on one day was because if we took a private car, left at 7am, we'd hit postiano for breakfast, amalfi for the afternoon snack, and ravello for dinner (obviously changing now).
Maybe we should leave that extra day to postiano + one other town. One thing to note with Pompeii is that the family will get bored VERY easily after 2 hours. It's happened after any site in the world (human tendency I guess). So it will be 3 hours max in Pompeii (not including travelling).