overnight train from Paris to Florence

Hi, Jan.

You can't book that train more than 4 months in advance and it requires a morning connection in Milan. There is no direct train all the way through. The overnight leg is operated by www.thello.com. It's not a particularly fancy train. The next leg is served by both www.trenitalia.com (the national railway) and www.italo.com (a private company). Some web sites will sell both tickets, but you need not book them together. Also, the greatest possibility for any major changes in schedule or service is usually at the mid-December Europe-wide schedule adjustment.

It can be cheaper to take a direct flight from Paris CDG or Orly airports to Florence (or other Italian airport). See www.skyscanner.com.

The Man in Seat 61 website is great for train travel. Here is a link to train options from Paris to Florence. As you can see, he has several options that might suit your needs.

https://www.seat61.com/international-trains/trains-from-Paris.htm#Paris-Italy

Good advice from Laura. For the comfort and convenience involved I'd opt for a direct flight from Orly to either Florence or maybe Pisa using the link she provided.
There are times when a train makes sense, but frankly this isn't one of them.

note that the timetables normally use the Italian name FIRENZE

The night train arrival at Milan is at 6:00 and even if you allow some padding for delay and catch an onward train after 7:00 you will be in Firenze quiet early. You could book the night train further to Verona to have more sleep and get a fast train from there, you'd be in Firenze by 10:30

For 4 of you the best option would be a 4 berth couchette compartment. These are simple bunk beds, there are washrooms at each end of the car. The slightly more luxurious sleeping cars have 3 bed compartments, fine for the boys but you would have to share with other women (or pay a huge premium for sole use) https://www.thello.com/Paris-Venise/Votre_confort/index.html