I would go through Zion National Park
We're planning a trip to Zion for September.
On our return trip we're going to be camping in Mather Campground which is located in the South Rim. I think .... our first trip to the Grand Canyon.
Ok Ok I can't talk you into the north rim
Regardless, if this is your first visit ever to GCNP you will be incredibly awed and inspired. I feel happy for you and your family... all this in a new egg too! Whoa.
As for place to stay on your way back to the bay area I can tell you that I would avoid the SJ valley any time I had an option to drive the Sierra (probably because I lived in Fresno six years and commuted every week to Livermore and back... as well as a half dozen trips to LA).
It looks like the halfway mark on your trip home via 40/5 will put you in Barstow and I have no idea where to stay there. But if you would consider a different route go north from Kingman, through vegas, and then on to Tonapah or Bishop. Then next day over the Tioga, through Yosemite and home. I can give you many good places to stay if you choose that route. It would be about 50 miles further and take a little longer but the things to see!and people don't drive so fast!
Cheers and Good Egging