Italy in May for first time

Pompeii can be done in a day trip from Rome, but it will be a long day. You have to change trains in Naples if you go by train, which is the least expensive way AFAIK. You'll need to watch the train schedule and not miss your connections.

Various tour operators offer day tours from Rome, with prices varying according to whether private (which might be a good choice for you since there are three in your party) or with a van/bus group. Some tours may also include a stop at Herculaneum, which is an interesting contrast from Pompeii.

You'll see Mt. Vesuvius from Pompeii when you're there. Realize that Pompeii Scavi (excavation) is an entire city, so there is lots to see and a lot of acreage to walk around.

As for your 3rd question, personally I'd take one of the Venice days and put it to Florence/Tuscany, but it's up to you.

Welcome to the forum Betty_lou-

Are flights booked? Any chance you can fly IN to Venice, OUT of Rome? It is just easier and Venice is a better place to get over jet lag. Early departure flights from Venice are a bit of a pain- not impossible just require more time and money.
However if your flight is past 11 am you should be oK.

So it looks like you have 15 NIGHTS total. That's a decent length trip as long as you don't go over board with location changes ;)

I think I would take a night from Rome and give it to Florence. If you want a Tuscany hill town day trip from Florence that takes a whole day.
Highly recommended here
toursbyroberto.com-- don't delay he books up early.

There are others Walks of Italy.com, Walk About Florence.com. Do book with the actual tour compnay- not with Viator or Get Your Guide, etc.- those are resellers.

Day trip to Pompeii from Rome is brutal, but doable. If this is a must there are a lot of posts here with info how best to do.

One suggestion, take one day from Venice and add to Florence or Rome (if you plan a visit to Pompeii add that day for Pompeii).

I agree with moving one day from Venice to Florence or Rome
My suggestion for your day trip from Florence would be Siena - take the Tours by Roberto tour of Florence .... one of the best we have ever taken. We did a good food tour in Florence on our last trip.

Thank you all. We have already bought our plane tickets so no changing. After reviewing we did take a day from Venice and added it to Florence.
Again thank you for all the suggestions.

Betty-Lou- I highly recommend an all day tour of Tuscany offered by Walkabout Florence, they have a tour called Best of Tuscany that includes lunch at an organic winery/farm. You will visit Siena and San Gimignano and Pisa. They drive you by air conditioned bus and you get a walking tour of each place and time to wonder on your own. They are highly rated on TripAdvisor.

https://www.walkaboutflorence.com/tours/the-best-of-tuscany-in-one-day-trip-from-florence

Thank you. We will look into the tours. Another question. All recommendations that I have read say to buy train and site tickets early. Do we have to have specific date in mind or can a date range be used?
Thank you

Do we have to have specific date in mind

You can save money getting high speed trains tickets in advance. In your case that means the trains from Rome to Naples, Rome to Florence and Florence to Venice. Unfortunately discounted railway tickets are train-specific and can be changed, if they can be changed, only paying a fee.

Since you are travelling before June 10, You can compare the schedules and the prices on the official sites of both railway companies. Remember that discounted tickets sell out, the cheapest ones sell out quickly.

Put May 31 as day of travel on trenitalia.com . Today you can pay a non-refundable/non-changeable ticket from Florence to Venice "only" 32,90 Euro per person, in Standard class. If you purchased the same ticket for the same train on May 31, you'd pay 57 Euro.

You can save almost 25 Euro per person by purchasing months ahead, but a discounted ticket will lock you into a specific time and date months in advance.

and site tickets early

Nobody can skip the security lines to enter sites and museums, but there is no reason to wait also in the line to purchase entrance tickets at the counter. Get the entrance tickets you want online and save vacation time.

Based on the input here regarding pent-up demand for European travel, I'd suggest you lock down your lodging asap. Have a wonderful family trip!

Unfortunately discounted railway tickets are train-specific and can be
changed, if they can be changed, only paying a fee.

I think Dario meant to say
"discounted railway tickets are train-specific and can't be changed"

Most would agree that Pompeii is a real stretch for a day trip. That’s definitely an “on the go” day, and logistics aside lands you in Pompeii for the hottest, most crowded time of day. It may wallop you early in the trip. I would save it for another trip. Ostia Antica is a well regarded alternative, and is certainly much easier day trip out of Rome.

You also might appreciate a day trip to Orvieto from Rome. While it is not a Tuscan hill town, it has Tuscan hill town vibes.

How far in advance can tickets be purchased? i.e. Colosseum? On website it does not let me put in May and it does not say how far out you can purchase.
Thank you

Glad you added a day to Florence. You won't be disappointed. Lingering at dinner and people-watching is a past time here. There are a lot of day tour options from Florence, including Siena, Pisa, Lucca, and more. We did that early morning flight from Venice and while it IS early, you can catch the bus from Piazzale Roma directly to the airport. To us, water taxis were more of a pain than it was worth. We stayed at the Antiche Figure which is directly across the canal (and over the bridge) from the train station. It was an easy early morning walk from the hotel to bus on departure day - for a 5 am bus.

I change airline tickets often. Since airlines are no longer charging change fees,there's no cost.
I just changed a flight for May 2 weeks ago.
Sometimes flying into one city and departure from another is cheaper.
For example Bologna which is around an hour from Florence is often quite a bit cheaper than Venice.
No harm in trying with the goal of making an itinerary better for the places you want to visit.

I am truly a micro traveler, so perhaps I have a different perspective. I would not make a trip to Pompeii from Rome. Pompeii deserves an entire day. I agree that Ostia Antica is a good alternative; you can leave from Rome’s Ostiense train station. I would also skip making a Tuscan hill town trip; take the bus from Florence to Fiesole which is less than a half hour. Fiesole is a typical Tuscan hill town. Enjoy Rome, Florence & Venice, and plan to return.

Thank you all for your input. I am enjoying checking into the suggestions and making decisions from them. We have deleted Pompeii for Ostia Antica plus we will relax at beach near there.