Recommendation for Just 1 Ticketed/Reserved Site in Venice

If the girls don't like museums, Basilica S Maria dei Frari may be a good cathedral to visit. Not as ornate as San Marco but interesting altars and niches, no advance booking and a small entry charge. Depending on where you are staying, you can walk across the Rialto Bridge, through the Mercato del Pesce (fish market) on your way there.
I really enjoyed Carlo Goldoni's House (it's on the way to Frari), a very small museum with period costumes, furniture and a room set up with Goldoni's puppet stage and puppet display.
Enjoy your visit to my favorite city!

I highly recommend the Secret Itineraries Tour of the Doge's Palace. We did the English language tour and it was very fascinating and educational. Your daughters would get a reduced price. If you are interested, book now.

I have passed the gondola boatyards (Squero) and often thought I’d like to see inside and learn more about gondolas. Something totally different, not a museum but a place where you can see the gondolas being built and repaired. Plus it’s an interesting area of Venice with a different sort of architecture. For info check on line at vivovenetia.com . Cost is €149 for a group of up to 6 and the workshop tour is about 30-45 mins. They offer a bunch of other interesting tours that your girls might enjoy.

I have not used vivovenetia but would considering doing so as they offer something a bit different.

Thank You all for your responses - I really appreciate your advice and recommendations!

I'll 2nd Secret Itineraries Tour of the Doge's Palace. My then 17 year old daughter really enjoyed it and the stories about Casanova and his escape.

If the weather is good, Row Venice offers rowing lessons on the quiet back canals, about 110 euros for all of you, total, for 90 minutes. It is harder than it looks, and you all switch out when one needs a rest. Best photos and experience!
Have a wonderful trip!

Think about the Palazzo Fortuny. It is sort of a museum, and it is also their house. The Fortuny family were into everything, textiles, fashion, theatre design. So the furnishing and articles reflect those interests. I have been several times over the years, one of our favourite places in Venice. Mercifully, not crowded.

https://fortuny.visitmuve.it/en/home/

https://artsandculture.google.com/story/palazzo-fortuny-palazzo-fortuny/ngUhtKyiz6dcIw?hl=en

The Basilica Frari church is fun. It contains arguably the most ugly monument in all of Venice. Four black gentlemen, bulging eyeballs, carrying sacks of whatever. On top of this is Doge Pesaro.

A little further towards the front, mounted on the wall is a small bomb. It fell on the Frari in 1918 and failed to explode.

I find the monument in the Frari to the sculptor Canova achingly beautiful.

No need to book the Frari. The café immediately over the bridge, Al Archivo, does a nice light lunch.

I would recommend a vist to San Marco Basilica and the upstairs area with the famous horses and the outside terrace. It doesn’t take long and it is amazing. Book skip the line timed tickets:

https://basilicasanmarco.skiperformance.com/en/store#/en/buy?skugroup_id=2524

And I highly recommend a visit to the roof top terrace of the new upscale department store, which the girls might enjoy . You must book 3 weeks in advance on the day the tickets (free) are released.

https://www.dfs.com/en/venice/service/rooftop-terrace

I would also vote for the Doge’s Palace. It has spectacular art on the walls, ceilings, a prison to visit, and a variety of rooms and furniture, and even some arms and armour. A good variety.