I've lived almost 30 years in CA, both north and south. A lot is going to depend on what you and the family want out of a trip. If it's major tourist stuff (Disneyland, the Bay Bridge, etc) in the cities that's going to be different than if you're more aligned with the more rural attractions (Yosemite, Redwoods, etc). Likewise, if you can delay into September it will be better than August, unless you really want multiple days with temperatures over 100f.
There are two basic routes I'd look at. First, to make the most of the cities, San Francisco to L.A. via the coast. Second, San Francisco to Las Vegas via hwy 395.
If you take the coast road you'll have time to spend in both the major cities, and a great drive from Santa Cruz, Monterrey, Big Sur, San Simeon, San Luis Obispo, Santa Barbara, and into L.A. This can be done in a days hard driving, but to really see the area two weeks is a start.
The other route I suggest would be S.F. , Sacramento, Lake Tahoe, Carson City, a detour at Lee Vining to Yosemite and Sequoia, Bishop, Lone Pine, Death Valley, and home via Las Vegas. This is one of the most beautiful routes in the entire USA., and if you like the outdoors this is the way to go. This is the California most tourists never see.
Pick a route, and once you know where and what you want to see or do, we can help with more specific suggestions.