Doge's Palace - Secret Itineraries Tour?

We did the Secret Itineraries and I thought it was well worth the money spent. The tour took us to secret rooms and corridors within the Doge's Palace. Got to see Casanova's prison cell and it was also cool to see a closet open up to reveal a secret passageway. Here's the website to book the tickets: http://palazzoducale.visitmuve.it/en/il-museo/percorsi-e-collezioni/itinerari-segreti/ You will end the tour inside Doge's Palace, thus you can still walk around the "normal" areas of the Doge's Palace.

Before and/or after the Secret Itineraries tour you can visit the rest of the palace on your own, with or without the audio guide (which I liked, by the way). The parts of the palace you visit on the SI tour are open only for the tours. I haven't taken the regular tour. The SI tour gives a lot of detail about daily life in Venice and the inner workings of the government. The rooms are much different from the rest of the palace: large, richly decorated rooms full of paintings. So I think the SI tour would be more interesting for kids.

I went to the website that Rick suggests in his book, www.museiciviciveneziani.it and tried to reserve tickets for the secret itineraries, but I couldn't figure out which tickets to buy.
I need one adult ticket and two reduced tickets for my two nieces that are 16 & 18 yrs old. There are two family options. One says Intero Famiglia for 20.50 euros and the other says Ridotto Famiglia for 14.50 euros. I want to make sure that I get all 3 tickets. Can someone help me out?

Is the cost 20 euros for just 1 adult ticket or is it an additional 14 euros for each student. The family ticket looks like it covers 1 adult and 2 students for 20 or 14 euros. I am confused at how many tickets I need to purchase.

The way I interpreted the site is that a family must buy 1 full price ticket (Intero) and then, as long as they buy 2 or more tickets, the rest are at the 2 lower (Ridotto) price. So, for me, my wife, and my 11 year old, I bought one Intero ticket and 2 Ridotto tickets. If I was wrong, I will look pitiful and figure, at worst, I might need to pay the difference.

Why not just call the helpline number?? I remember calling them asking about the reduced price for 2 adults if I held museum passes. Operators spoke decent English and was able to help me out.