I get it that you probably don't have a choice but to do your southwest swing in July. But that is the worst time of the year to do it, if you want to avoid crowds and heat and have flexibility to make impromptu route changes. We did Zion last year in October. And we did Arches, Canyonlands, Mesa Verde, et al. this year in early May (before the Spring Break crowds).

My wife has mobility issues so we did very little walking in Zion and still really enjoyed it, spending a couple of days. To me, the shuttle buses are a feature, not a bug, although in July I suspect that there are long lines to wait for them. (In October there was almost never a wait.) Two things I would do that are near Zion if they are on your route are Cedar Breaks National Monument and the drive to the top of Brian Head. Both of these can be done quickly, yet have big scenic payoff.

For the part of your trip in the MV area, I guess you need to decide how much focus is on recreation and scenery (e.g., river rafting) and how much on education (e.g., learning about the topography and ancient cultures of the area). Our initial planning was for balance, but as it worked out, we did MUCH more on the learning side than we expected, such as going to the Canyons of the Ancients museum in Dolores, Colorado. I guess it depends on the ages of your kids and their personalities but that museum if EXCELLENT! It has ancient dwellings that you can easily hike to right from the parking lot.

We did not go to MV on our trip last month because we did Valley of the Gods instead. And it was certainly one of the highlights of our vacation. If you go there, don't miss driving the Moki Dugway. https://www.tripadvisor.com/Attracti...gway-Utah.html