Hello feiliao,
I will agree with other posters that you probably have too much in this schedule. It is not that you couldn't do everything listed but everyone is not into all the activities it just may not be enjoyable.
My first piece of advice is to allow some room to breathe. Remember that you need to eat and rest and explore the unexpected and get from place to place and get lost and then found again.
If I flesh out your first day:
Train from Rome to Florence
(Get to your hotel - figure out taxi, bus, tram, walking? Florence train station is a thing)
(Check-in, drop your bags, get ready to go out)
(Get to the Uffizi - bus/walk?)
Uffizi Gallery (reserved tickets at the Uffizi are timed you'll need to make this appointment)
(Lunch? Before Uffizi depending on time)
Museo Galileo
(Gelato)
Ponte Vecchio
(walk/climb to)
Piazzale Michelangelo
(Dinner)
(Get back to your hotel - collapse)
Honestly sunset at Piazzale Michelangelo is a cool thing but you'll probably share it with 3,000 other tourists like we did. If you manage to get everything else on your list I'd swap out for walking across Ponte Vecchio and wandering down towards Santo Spirito and having dinner instead. For the hike/taxi ride up and back to viewpoint I'd trade that for an easier night on everyone.
Depending on your interests - but especially with a 12 year old along - a string of Museums and places like the Pitti Palace can become a string of "a lot of the same art/old stuff" and it can quickly become less special. And there will be a lot of walking. A lot of walking and then dome/tower climbs on top of that. It is easy for group morale to drop when tired, hungry, bored and it's important to keep the level of interest up.
As others have pointed out unless you have a real interest in architecture you probably don't have to climb every feature in Florence. Or maybe you can split them up so you climb the Dome and the other has gelato with the 12 year old and then they climbs the tower while you do something of more interest on the ground.
I know it seems like a shame to miss anything but there is too much in Florence to see in five days let alone the 2.5 you're planning on. I'd make a list, make some hard choices and leave some things in the "if we're feeling up to it" category.
Reserve the date and time at Uffizi - the Passeporte ticket also gives you access to the Pitti Palace and Gardens - and at the Academia for David if those are the the top two on your list, Duomo tickets are untimed except for the Dome climb so you have some freedom for when you decide to go. I'd concentrate more on everyone enjoying their time in the city and knock a couple of things off your list.
As RS says "Assume you'll come back. You don't have to do everything right now."
My $.02, have a great trip,
=Tod