itinerary for 3 days in Rome

I'm not sure what you're counting as Day 1 but this is what I'm guessing:
Day 1 Arrive and settle in: Saturday, July 19th
Day 2: Colosseum: Sunday, July 20th
Day 3: Vatican/Sistine: Monday, July 21st
Day 4: Pantheon/Trevi Fountain: Tuesday, July 22nd.

Yes, it works except for Day 4: Trevi is just a walk-by that can be done early/late any day other than maybe the Vatican. Pantheon should be combined with the Colosseum as it's reasonably nearby. That leaves you with a full day (Day 4) for other attractions. What are you interested in?

As well, if you're doing the Colosseum I'd strongly consider doing the Forum and Palatine as they're included in a Colosseum ticket. I'll go even further in recommending a guided tour that includes the Colosseum, Forum and Palatine as they're all so important to the Roman story, and that the Forum and Palatine are more difficult to understand on your own.

Day 1: Colosseum

Get the Colosseum tickets with Forum and Palatine Hill directly from colosseo.it. Do the Colosseum, then go have a nice lunch nearby, followed by touring the Forum and Palatine Hill in the afternoon. You can download a free audio tour for each half of you day here on Rick Steve's and they are excellent tours. No need to pay extra for a tour guide so you can spend what you save on eating somewhere with a lovely view for dinner like Aroma Restaurant or just go to The Court for aperitivo at the end of your day.

https://www.ricksteves.com/watch-read-listen/audio/audio-tours/italy

Day 2: Vatican/Sistine Chapel

The Sistine Chapel does get very crowded so consider whether booking the earliest morning entry you can find might be worth it to you. Last time I was there I did this. Our group got to see them unlock the Chapel and had around 8-10 minutes in there with just our small group of 12. It was absolutely breathtaking, and so worth the expense so I always recommend it. You can leave the Chapel when it gets crowded and go back to the Vatican Museum, or take the hallway to St. Peter's. Unless you're going back to the Museum you will have some time to do something else that day. The Heart of Rome and the Jewish Ghetto walk audio guides are excellent if you have the time after seeing whatever you go to see on any day.

Day 3: Pantheon/Trevi Fountain

Unless you're leaving Rome by noon you'll probably have time to do other things on this day. If you go by the Trevi Fountain very early in the morning you can avoid the crush. The free Rick Steves Audio Guide for the Pantheon runs about 25 minutes, but entry takes a bit of a wait even with getting there an hour before the opening in my experience. You could also see the Trevi before or after dinner on one of your other days since it is open nearly all the time.

Thank you so much for the suggestions and advice. It looks like we will have plenty of time on day 4 to see other things. Are there any suggestions? I don't know enough about what there is to do in Rome so I am open to anything!

Hi there, lots of good advice above. I will add that the Trevi fountain is much quieter first thing in the morning than later in the day. I would go there first & then walk over to the Pantheon and use RS's audio guide as recommended above. I know tickets are required to enter the Pantheon now, but don't recall how that works, use search bar above? Note that the highly recommended early entry to the Sistine Chapel is very expensive, I seem to recall reading $400 per person, but it's easy to find. Personally, if someone ever drags me back into the Vatican museums, I would be delighted to pay that to be spared the crowds. HA.

I wondered if you've taken the heat into consideration, on cobblestones, tired, need some breaks and maybe a siesta? Consider researching restaurants near the sites you're visiting so you have an idea where to stop for lunch. My last TR has some recommendations for restaurants. I bought a sun umbrella for my next Med trip, you might consider them for your gang.

Day 3 you may have some more time, but whether after the Vatican Museums and St Peters you can handle standing longer or going elsewhere is another matter. (See my comments below about underground museums, if either of them are near your hotel.) I think you will need GELATO! IF you can stand another attraction, Castel S'Angelo is very close to the Vatican, maybe a 15 minute walk. On the highest floor there was a cafe, great views, not sure if it's still open.

You will have more time on Day 4, but whether you have more energy for another museum or standing out in the heat is another matter. We visited 2 subterranean museums in Rome, both of which will be much cooler than being outdoors - one close to the Trevi Fountain, with water rushing under your feet, part of an ancient Roman villa, very cool, (this needs reservations, see in my TR for details, you Whatsapp them a day before). The other just around the corner from Piazza Navona, part of an old Roman theater, just bits and pieces but quite a fun exhibit. They're both explained in TR below. We really liked the tiny pizzeria by the slice mentioned in TR, close to Trevi fountain. https://community.ricksteves.com/travel-forum/trip-reports/rome-was-jammed-over-ny-but-still-fun.

Churches - There are some amazing churches in central Rome, with incredible art work, (you need 1-Euro coins to light up the art) , the interiors tend to stay cool and they could offer a nice break. San Clemente, (needs reservation for the scavi below,) St Ignatius de Loyola & Santa Maria in Trastevere (don't miss the ceiling mosaics!) are all lovely, and there are many others.

Another option I have not done personally, would be to take a golf cart tour around the historic center at nighttime, when all the amazing lights are on the Capitoline museum and down the Foro Romano to the Colosseum. OR if you can stand more walking, take an evening food tour, the sunset tour of Trastevere by Eating Europe gets rave reviews. Have fun!

PS, You asked for other ideas on Day 4, had you considered the Galleria Borghese? It's by far our favorite museum in Rome, but really you may need a break from museums, which is why I suggested the subterranean exhibits above.

With the new 8 AM opening time for the Vatican Museums, there are no reasonably priced tours that get you to the Sistine Chapel before the general public. There are some very small tours that do that, but the price is very high--many hundreds of euros per person.

The only way you can go through the door between the Sistine Chapel and St. Peter's is if you're on a commercial combination tour and you follow the guide through that door. The door cannot be used by individual travelers or by the Museum-only tours provided by the Vatican itself. You cannot go back into the museums after seeing the Sistine Chapel and later go through the shortcut door. It's quite a walk from the Sistine Chapel to the exit, and then a considerable outdoor walk around the building to St. Peter's, where you'll find a shockingly long security line. With luck that security line will move pretty rapidly; I can't comment on that one way or the other, because I took one look at it and gave up. The next time I'm in Rome, I'll try to get over to St. Peter's before 7 AM and hope for the best.

Thank you, again!! You all have helped me greatly! I am going to look into everything and book as much as I can, as early as I can. I see that we will have to be prepared for long lines/waits in the heat! :(

For the Colosseum, I highly recommend getting the add-on to visit the attic (attico). This is exclusive access, via elevator, to the very upper levels of the colosseum. We just did this a couple of days ago and it was amazing. We had an early time, 9:10 am. When we entered the colosseum, we had someone point us in the direction of the access to the elevator. They told us we had 30 minutes to visit up there, but honestly no one is up there with a stopwatch. We spent more than that up there and the best part was, there were literally 7 other people up there with us in total. We had the entire upper levels to ourselves.

We finished that and went down to the main levels to confine our visit and the crowds were crazy. Every spot that had a good place to take a photo was mobbed. Waking was slow because or the crowds. (Even in February)

But none of that concerned us because we had literally the best views to ourselves up top with no one else around.

Near the end of our visit, we looked up to the top levels where we started in the attico, and there were still only a few people up there. They must only sell a very small number of tickets per time slot.

I did have to book the tickets exactly one month in advance when they went on sale. And each time slot goes on sale at the same time (Rome time) a month earlier. This meant that on the US east coast, I had to be awake and online at 3am to start trying to secure 4 tickets. I missed the 9am slot but got the 910 am (at 310am local time for me).

Highly worth the effort. One of the most unique and uncrossed experiences of our week so far.

Thank you, juice06870! I am going to set my alarm now to book tickets! Luckily, I'm on the west coast so I just have to stay up until midnight. :)