Tuscany tour?, Umbria stay and sights

Hi and welcome to the forums!
Off top of my head....

When we land in Rome we are going to take train to Florence and spend
3 nights. Then I was thinking of a day tour around Siena, Chianti, San
Gimignano

3 nights are only going to give you two full sightseeing days + a few potentially jet-lagged hours in Florence upon arrival. It's a city with a wealth (!!!) of historical sites, religious sites, museums, etc. so I sure wouldn't use one of those only 2 days to leave town.

...looking for a place(s) that is easily accessible by train and
walkable. Assisi, Ortievo?

Orvieto has been a popular choice with many forum posters who've stayed there. Your daughter (and rest of you) might enjoy riding a rental bike around the city walls. Easily accessed by train.

After that we will be returning to Rome for remainder of trip...

For how many nights? That's another one with umptybumpty things to see so my personal recommended minimum is 4 nights/3.5 days.

Is there an app or a pass for train tickets? Do I need to purchase
ahead of time?

Not really. There can be a benefit to purchasing tickets for the "fast train" journeys - such as Rome to Florence - in advance but only to land discounted tickets when available. That can be risky for arrival days as a flight delay can cause them to be unusable. There are some ways around it but just buy when you arrive. You are also not taking many journeys (Rome>Florence> Orvieto>Rome) so I'd just buy point-to-point tickets when you get there, and as you need them. You'll have an assigned carriage and seat for the "Fast trains". Regionale trains - which you might use from, say, Orvieto to Rome, are sit-wherever. Those also have a pre-boarding phone check-in process for Etickets bought online via app so it might be easier to buy paper tickets at the station and just manually validate them before boarding in the time-stamping machines near the tracks. No wrong way; whatever works for ya. :O)

Italy's national rail service:
Trenitalia: https://www.trenitalia.com/en.html
You must use the Italian names of the stations such a Firenze SM Novella (main station in Florence) and Roma Termini (main station in Rome). There is a train that travels directly to Florence from Fiumicino at 13:53 but otherwise you'll be changing trains in Rome.

ItaloTreno serves both Rome (not the airport) and Florence so that's your other possibility for arrival day, depending on which company offers schedules that work best.
https://www.italotreno.it/en

Those museums and historical sites? You're going to want to order advance, timed-entry advance tickets for the most-visited of them, such as the Uffizi (Florence), Colosseum and Vatican Museums (Rome), climbing the dome of the duomo in Florence, etc. as both cities promise to be very busy. Do you have a rough sightseeing plan?

Wow! Thank you!

We thought going to Florence first gives us a couple hours to sleep on train. I know two days is not much there but hopefully we can make best of it. We are used a packed day and walking many many miles in a day.
Bikes might be a fun idea, my husband will love that.

We will have 4 nights in Rome. Planning on Vatican on our last day. As far as things to see we do have a list but would like to just wonder a bit too.
I still have a lot of planning. I appreciate all the tips!

Alternate idea
Head to Orvieto on arrival
It’s closer to Rome ( about an hour)
And a nice place to get over jet lag
Served by regional trains
Spend 2 nights
Then Florence 3 and back to Rome for 4

That way your short time in Florence won’t be jet lagged

Orvieto is in Umbria
I don’t see how you have time to explore any further

For Umbria I'd recommend staying in Perugia. It is larger compared to many of the other hilltowns in the region and has a minimetro up to the top from the train station. From there Assisi and some other towns can be reached by train. We've traveled in the region by train and the catch is that their schedule is your schedule; rather than being evenly spread out over the day the times may be bunched so your choice may be to spend 2 hours or 5 hours in a town reachable by rail. Perugia is also the regional center for transit if you're a bit more adventurous and want to ride buses; the staffed TI on the hilltown is very helpful and can help you make sense of the bus schedules.

It's been a few years since we were in Umbria but at that time in the smaller towns the ticket machines were not the modern Trenitalia ones with a touchscreen and English menu but older ones all in Italian and a bit harder to use. And most stations are not staffed. If you'll have data on your cellphone I'd highly recommend the Trenitalia app (when the conductor comes around to check tickets, for a Regionale train you need internet access to retrieve the ticket). For Regionale trains you need to check in the day of travel; it's not hard, just search online for discusssion/demo. If you're getting the app then install it now and create your account. As a hint, you'll need to use the Italian name for the USA on the pulldown when entering your address. Train passes do exist but almost never come out cheaper than buying as you go.

In Rome we did a food wallking tour and thought it was great.

Again thank you for great tips/ideas. I wish we had a month to spend, but I guess we have to just make it back to Italy another time.

I have an Airbnb already booked for Florence, can still cancel and change. My thought was Florence and Rome will both be lots of walking and much to take in so break up with Tuscany tour and Umbria in between. Thanks again

We just spent 10 nights in Florence with some day trips.

Highly recommend this tour guide. He does tours in Tuscany and Florence. We only used him for a Uffizi tour but had I known he was this great we would’ve used him more.

https://guidaturistica-michelebusillo.com/

I will check that out. Thank you. What tours from Florence did you end up doing?

What tours from Florence did you end up doing?

I recommend spending at least two days in Florence. Depending on how much time you have, you could do one or two day trips. The first I would recommend would be a day trip to San Gimignano and Volterra. I've seen day trips listed for Siena, San Gimignano and Volterra, but I think that's too much for one day. You won't have enough time at any stop. If you have another day, then take a trip to Siena.

I hope you have a wonderful trip! April will be a nice time to visit. Your mention of your 15-year-old daughter made me think of my first trip to Europe when I was on a high school trip when I was 15. There were four boys and four girls from our town. There was a 14-year-old girl in the group and we started hanging out. We shared our first kiss in Florence and have been going steady ever since, getting married when in college. That was 53 years ago and have made many trips to Europe together since then.

That is a wonderful story! Thank you for the advice. We are splitting our time between Florence and Rome with possible day trips.

I love both Tuscany and Umbria. However, since this is your first trip to Italy, focus on Tuscany and spend a few nights in Siena, using it as a base to explore the charming, nearby towns. Consider renting a car for Tuscany which we always do.