I always said I would never visit Italy in the heart(heat) of summer, but.....

We’ve done a more extensive trip only across northern Italy. With 10 days pre Siena and your desire to be in the Dolomites maybe something like this would be good with a day trip thrown in based on your family’s interests.

Fly into Venice (2 nights)
Train/bus to somewhere in the Dolomites (3 nights)
Train to a lake (3 nights)
Train to Siena (2 nights)
Fly out of Pisa, Florence, wherever…

Keeping it relatively cool in July!

I must warn you that I had a great deal of trouble finding affordable lodging on Lake Como (beginning August 30) and in Bolzano (which is down in a hot, low-lying valley, not up in the mountains) for early September.

Verona is a possibility, but the opera festival drives up hotel rates there. Padua has some interesting sights and usually has much less expensive lodging options. A couple of places between Verona and Venice recommended by others are Treviso and Bassano del Grappa; I haven't been to either yet. Edited to add: I should have mentioned that those two towns are north of the main Milan-Venice rail line.

If you flew into Milan, you could consider time in Bergamo and/or Brescia before going to the Dolomites.

Alternatively, you could hit the Dolomites and then go to Bologna, which offers some very attractive side-trip options.
 
I adore Ravenna, but I'm not sure it makes much logistical sense in combination with the Dolomites and Siena on a short trip.

Personally, I wouldn't recommend flying to Venice and spending just two nights there. You'd only have one full day in the city, and some members of your family might still be off-kilter on that one day.

Ortisei in the Dolomites is a great location and the lift served hiking would appeal to those less physically inclined as well. Three or four days there would be perfect followed by a couple days around Lake Como before heading to Siena.fly in and out of Milan for some additional big city time if you need it.

How about Lake Garda in addition to Dolomites? I was going to have 5 nights in Dolomites and 3 in Lake Garda this year but will have to wait. But very doable.

I would also suggest looking into Lake Garda - particularly Malcesine. It is touristy but that's because it's charming and in particular it has a cable car up to Mount Baldo for hiking around or back down to Malcensine or up if you want a real challenge. The Malcensine to Mount Baldo hike is 6.6 miles and gains about 5,500 feet. You can also use the upper lake ferry to visit the other towns around the lake.

Have a great trip,
=Tod

Thank you all so very much! Your suggestions have saved me hours of my initial research. I'm thinking of adding 1-2 days onto the itinerary.

How is the drive to Ortisei - very scary? I see that there is a train from Venice but I've read in so many places to rent a car for the Dolomites.

It seems like we would either fly into Venice or Milan. I think Venice fits us better than Milan if I had to choose right now....although the report of heat and crowds does give me pause for Venice. (I do understand we will have crowds probably everywhere).

There's good bus service from Bolzano up to Ortisei; that's the way I traveled, and I don't remember a particularly challenging road. Before you get to Bolzano you are not in the mountains, so I think it would only be traffic you'd need to think about.

I believe you'll find a lot of people have been to the Dolomites without a rental car, though if you have very specific areas where you want to hike and there are few or no bus connections, that would be a good reason to have a car. But there are lifts as well as buses to get you to a lot of good hiking areas.

Fly to Venice VCE:
Venice: 3 nights
Rent a car in Venice (Piazzale Roma) at the end of your Venice visit. Drive to Dolomites. I suggest drive to Cortina then to Ortisei via the Pordoi Pass and the Sella Pass. That drive without without pit stops is a bit over 2 hours but of course you will stop for photos. It’s about 30 min longer than going through the Valparola pass but I think it’s nicer.
Ortisei: 3 nights, would be best, but at least 2 nights are necessary to have a full day for hiking.
Drive down to Siena. If you want you can stop at Lake Garda along the way (slight detour after Rovereto). North Lake (Malcesine, or Riva, or Limone, or anyplace in the north lake). Lake Como would be too much of a detour and finding accommodations in July would be even more difficult than Lake Garda.
Lake Garda: 2 nights
Drive down to Siena.
Siena (Tuscany): remainder of your available nights except for the last night, which you must spend closer to the airport of departure. Florence airport would be closest, but otherwise Rome. Don’t bother with Pisa. In the time you need to get to Pisa from Siena, you can drive to Rome airport, where you have more flight choices and lower prices (and possibly non stop to your home airport, but you don’t say where your home airport is).

The above is a very rushed trip, so if you can make it a longer vacation it would be better. The ideal would be 3 nights in Venice, 3 nights at the Dolomites, 3 nights at Lake Garda, 4 or 5 nights in Tuscany (Siena) so that you can squeeze in a few day trips, including to Florence. Rome of course deserves a very very bare minimum of 3 nights, in case you want to add that too.

July is super hot, although not necessarily muggy (certainly not as muggy as Florida or even Washington DC). Since there will be 4 of you traveling and going to areas that are rural (except Venice), I recommend a car in your case. Having to schlepp suitcases on and off trains with temperatures in the 100s F would not be ideal to me. At least a car will have a trunk for the bags and air conditioning, besides being more efficient for the locations you intend to visit. Trains are best if you visit cities (no car needed in cities), but for rural areas and small towns, a car is more efficient, and cheaper for 4 people (trains aren’t free, especially the high speed bullet trains).

I am in the process of planning our 6th hiking-focused trip to the Dolomites.

When I saw this post, I started thinking about what I would suggest to you for that and the trip down to Siena. But I had a brunch for friends to cook, so did not post right away. And now Roberto has already suggested exactly what I would have. So I will just add some suggestions for Ortesei, and a possible recommendation for your Siena stay.

With a group of hikers and non-hikers, Ortesei is perfect. Or the adjacent village of Santa Cristina—- not really a charming village like Ortesei, but some excellent lodging options, with or without swimming pool. Definitely spend 3 nights, so you have two full days for hiking, one on either side of the valley. Non-hikers can enjoy riding the lifts up to Alpe di Siusi and the slopes of the Puez-Odle group on the opposite side, for great views, a nice lunch at a mountain restaurant, and easy strolls, while you enjoy your more strenuous hike.

I can post back with hiking suggestions later, when your plans have firmed up.

Lago di Garda makes a perfect next stop; we like Malcescine at the north end (we will be there in September), but there are other good options. Many of the hotels will have minimum stay requirements in mid-summer. Plan on 3 nights here.

For Siena, I will just suggest an agriturismo just outside the city that has 6 swimming pools of various kinds. Crowded on weekends but not too bad mid-week,mar least when we stayed there.

https://www.mulinodiquercegrossa.it/en/index.html

Look it up on booking.com for more photos and reviews. I cannot post that link because it is too long.

Another vote for Ortisei. You can take the lift up to Seceda https://www.ladolcefitvita.com/guide-hiking-seceda-italy-dolomites/ or to Alpe di Siusi on the other side https://www.val-gardena.com/en/alpe-di-siusi-italy/
Your family can hike as little or as much as they want to with you. There are huts along the way to stop for lunch or a beer as you marvel at the absolute majesty of those mountains. Driving there from Venice takes a few hours and is easy. I’ve done that three times and I don’t consider myself a super adventurous driver. This brings me to my last point, I would vote to add Venice. Stay in cannareggio. It’s a little off the tourist path, but a five minute walk to be right in it.

Thank you all for the additional replies! This is a wealth of information and I am grateful for all of it.