We (2 adults, 13 YO girl, all Aussies) went to Las Vegas last year for TAM, then drove down to Phoenix via the Hoover Dam, Grand Canyon and Sedona. It is the reverse of your direction, but some of that trip may be useful to you.
We all loathed Las Vegas - just not our sort of thing. Even the walking round looking at the sights, “gee it’s all OTT isn’t it? Look at the people” just didn’t sit well with us. Though there was a sound and light show in a street converted to a mall with overhead screens that we enjoyed. But, by and large, Las Vegas actively didn’t appeal to us.
Hoover Dam was interesting - worth a visit if you are in the area.
Grand Canyon. You could spend a week and not exhaust the possibilites. We had 1.5 days. We stayed at the south rim of the Canyon. I left the booking a bit late (only 2 months ahead of the visit!), so couldn’t get a room at one of the Rim hotels, but rented a room at one of the non-rim hotels in the park. It was basic, and the food at the general park restaurant was poor quality. If you plan to stay a night (which is a very good idea and the absolute minimum time), do yourself a favour and book and eat at one of the rimside hotels. If you can’t stay a night, just do a helicopter tour and leave the ground tour for another time.
We picked a spot along the rim to watch the sunset and booked in for the dawn tour. This was most excellent, and if we were in the Canyon area again we would do it again - and we are NOT morning people. If you have more time you can do mule tours down to the base of the Canyon, or walk, and I think there is also accommodation further down, but I don’t think you have the time to try that. A decent visit to the Canyon would take many days to really sample all it has to offer.
One thing we lucked on was that Canon was doing free photography workshops. If you don’t have a camera they lend you a top-of-the-line DSLR (you leave your credit card as hostage) and a professional photography instructor takes a group of you for a walk amongst the scenery and gives you tips on general DSLR photography, scenery and macro/plant/insect photography. Absolutely worth it if it is still running. If not, I think Canon was planning to run the workshops in other US National Parks, so keep an eye out.
Once we were well south of the Canyon and into the red rock country the drive was precipitous but gorgeous.
The Canyon was impressive, but ahhhhhh - Sedona! The woo capital of the South West, but so, so beautiful. If you have the time, go to Sedona and spend a couple of days. (We were discussing earlier today whether to go to TAM again this year, and the consensus was that any trip to TAM would have to be counterbalanced by another trip to Sedona.) You can ignore the woo, but not the beauty. We stayed at a hotel on the rim of a mesa with the whole town laid out below us. There was a cafe in town that made great sandwiches, and we sat on our balcony, cleansing ale/lemonade in hand, ate the wonderful sandwiches and were at peace with the universe several nights in a row.
We also took a jeep tour/hike out through the rocky areas - again well worth it. Take more water than you think you could possibly need.
If this is of help, I will gladly send you specific details.