So many great ideas above, and I'll agree that you really don't have many gaps for a service to fill! But, as Laurel said, sometimes it's just nice to have help taking care of any loose ends so look into the resource she recommended, and tousbyroberto.com as recommended by Christine for the Tuscany piece. I believe Laurel has used him as well?
Murano/Burano: Sure. I guess I sort of consider them as "Venice" even though they're not. :O)
Florence: for your "Explore on our own" time, hike your tribe up to Piazzale Michelangelo for a terrific view of the city, and up even further to the church of San Miniato (free) and a browse through the attached (and interesting) cemetery. There are some outdoor cafes near the piazzale too for kicking back with a beverage.
https://www.visitflorence.com/florence-churches/san-miniato.html
https://www.visitflorence.com/florence-monuments/piazzale-michelangelo.html
Rome:
Pompeii is a slog from Rome, although people do it. I'll agree with the others with doing Ostia Antica instead as it's so much closer and won't chew up as much of your day with transport time.
Another idea? Bike (or hike, as we did) a section of the Appia Antica. We did it on our own but as you're already sort of overwhelmed, I'll recommend booking a tour. There is a lot of interesting stuff to be seen along this ancient - and still used! - road, and your young people might enjoy the adventure on wheels. One resource:
Top Bike E-Bike tour (Top Bike is endorsed by Mr. Steves himself):
https://www.topbikerental.com/nuovosito/eng/tour-rome/ancient-appian-way-catacombs-and-roman-aqueducts-in-rome-italy?gclid=EAIaIQobChMIsvSamIqL_gIVmubjBx3stAw1EAAYASAAEgIt1fD_BwE
Laurel and I chatted about that one for a poster a few years ago, and that thread contains a link to a youtube video of their longer tour:
https://community.ricksteves.com/travel-forum/italy/topbike-rental-rome-appian-way-tour-long-or-short
The park's website:
https://www.parcoappiaantica.it
(click the "SMART INFO EN" text in the menu for English) or use your device's translation function.
Helpful map of the sites along the way:
https://www.parcoappiaantica.it/wp-content/uploads/2016/05/AppiaAntica_eng_2015.pdf
LOL, more than you wanted to know but it's a really interesting piece of Rome that most visitors don't allow time for. :O)
As suggested above, Galleria Borghese is a much easier museum for non-museum lovers to digest as it's smaller, on a 2-hour time limit so it doesn't chew up the amount of time the Vatican takes, and (best of all) has excellent crowd control: the mob at the Vatican Museums has become pretty horrible. The Bernini sculptures alone - Sorry, Michelangelo, but my favorite "David" is here - are well worth the visit. Along with the art, take note of the trompe l'oeil decoration of the various rooms. It's pretty wild!
If you DO decide to do the Vatican, book an early entrance tour through Walks of Italy, the Roman Guy, the Vatican itself, etc. But the other plus about the Borghese is exploring the many corners of the very large park it is located in (Villa Borghese). Bike and pedal-surrey rentals are available (google Bici Pinico, Villa Borghese)
Advance booking is mandatory for Galleria Borghese:
https://galleriaborghese.beniculturali.it/en/
Lastly, yes, I'd do the food tour on a different night than your last one in Rome.