Hi Mitch; welcome to the RS forums!
We see a LOT of questions about the AC, and opinions will be all over the place. Is it sort of a challenge to get around? Yes, a lot of that simply because the mountainous terrain limits the options, and that the place has become overrun to the point of all those bodies packing what public transport there is...which was likely perfectly adequate before it became a 'thing' for so many visitors. In fact, they've had to limit access by non-resident vehicle (such as a rental car) during parts of high season due to congestion of the single coastal road.
You are going at a little less busy time of the year so you have that in your favor. Yay. Still, weather is going to be a crapshoot, and ferry services will be limited; probably the most frequent that time of year will be between Capri and Sorrento as islanders need to be able to access the mainland. They may not run at all if the more extreme weather/wind makes sea voyages too dangerous.
Capri: yes, I'd definitely do that one with your teens but manage the expectations where the grotto is concerned. It's more likely than not to be closed in March, and even if open I'd read through reviews for the pros and cons before putting it on your must-do list? We skipped it and were never sorry but it's your trip so....
I would do the chairlift to the top of Mount Solaro, and there are any number of fun hikes to keep active teens occupied; no tours needed (ignore the touts for those on the Capri website), just get a map at the tourist office and follow the directions in these links. I'll personally recommend the route to Villa Jovis, and Pizzolungo. Not all restaurants and shops will likely be open yet but take a stroll through the two villages for the scenery and whatnot.
https://www.capri.com/en/e/monte-solaro-high-drama
https://www.capri.com/en/e/the-villas-of-tiberius
https://www.capri.com/en/e/pizzolungo-2
Others:
https://www.capri.com/en/experiences?from_landing_id=54
Obviously this is a good-weather activity. That's sort of the issue with the AC in general: it's virtually an outdoor sightseeing destination so if it's pouring buckets +windy+ chilly, there's little to do.
Pompeii: not the AC but honestly, I think this is a MAJOR reason to visit the area, and especially good for you as you'll miss the heat of the later spring/summer/fall seasons. Even if your teens don't think they'll find it interesting, I'm betting that they will. Yes, look at the Mondo "Pompeii Walk" tour endorsed by Rick Steves, and you can do further exploring (the place is vast) after your tour wraps up. We done it independently and couldn't cover it all in 5+ hours (and that was my 2nd time.) Get to the site by local commuter train; very easy and inexpensive, and we can give you some pointers on the thing if you decide to do it.
https://www.sharedtours.com
https://pompeiisites.org/en/
https://pompeiisites.org/wp-content/uploads/Pompeiweb2023.pdf
https://pompeiisites.org/wp-content/uploads/A-Guide-to-the-Pompeii-Excavations-2.pdf
Just the two activities above plus exploring Sorrento could easily occupy the lion's share of your time. If you decide to explore more of the coast, I'll vote with the others to skip Positano and head to Amalfi/Ravello.
