We did a West Coast trip last August as we're tied to school holidays too. The only places I found the heat to be really unbareable were Death Valley (obviously!), las vegas, lake havasu and hollywood.
We flew to Vegas and spent three nights there one would have been enough as we're not gamblers and the hotels start to feel a bit shopping mall after a while. But we had great evening meals and enjoyed circ du soleil.
Then drove through death Valley- amazing sights and would do it again despite the heat. We had two nights in mammoth lakes which was a laid back feeling mountain town with nice walks and outdoor activities.
We were then supposed to go to Yosemite but the park was closed due to wildfires so we went to lake tahoe instead. We didn't enjoy it but that was probably because we knew we were supposed to be in yosemitte.
We then did three nights in san fransisco. The food was great, alcatraz was great and fisherman's wharf for the touristy stuff. But the city was very dirty and the number of homeless people was quite sad. It was quite cold as the fog came in on day two and stayed.
We then drove down highway one which was amazing, but again cold and foggy in the morning. We stayed one night at monterey and one night cambria. Both were nice, but cambria was very quiet.
We then did one night santa monica which was nice for beach/fairground. Venice beach was... Interesting...
We did three nights hollywood which we didn't enjoy and wish we'd just skipped and spent more time in national parks.
Then two nights san diego which was nice, has a zoo, a big air museum on an old war ship. It felt a lot more relaxed than Hollywood.
One night at lake havasu for dp to see London bridge. But it was very humid there and nohhing else to do!
Then two nights grand canyon which was fantastic.
Then back to Vegas for one night to drive home!