We're hoping to go to San Fransisco (to see the Disney Museum) for a few days then drive to Los Angeles for the rest of the holiday. How long will that take, and what's the weather usually like at that time of year?
September/October are very warm months, and in San Francisco that time of year is the warmest. It can be foggy and 62 in San Fran in July, but in October it's usually sunny and 85 to 90. Check out the weather forecast for San Francisco this week, and it's sunny and 89 for several days, much warmer than it is there in the formal summer months of June-August.
http://www.weather.com/weather/today/San+Francisco+CA+USCA0987
You can drive from San Francisco to Los Angeles in about 6 hours if you take I-5 straight down, but honestly it's not much fun as you are on a freeway through an inland valley the whole way. Most of the trip you get a view like this on I-5 to LA, with occasional stops for gas...
But if you take the coastal route on Highway 1, a smaller and older highway, you'll get far better scenery and tons of activities and sights to see to fill up two days of travel. The highway travels right along the coast for much of the journey, and it's stunning.
Along Highway 1 from San Fran to LA you get many funky beach towns like Monterrey and their excellent aquarium and canning industry...
Carmel-By-The-Sea south of Monterey and is an amazing little town with famous restaurants and fancy shopping in this village with cobblestone streets, with more breathtaking coastal scenery and sweeping vistas from the road
Further south from Carmel you get to San Simeon and the famous Hearst Castle, the estate that William Randolph Hearst built with his publishing fortune and that hosted famous celebrity parties with silent film stars of the 1920's.
They offer tours of the grounds and show you the lavish ballrooms and dining rooms and fancy indoor swimming pools where Charlie Chaplin and 1920's Hollywood starlets socialized.
As you approach Southern California, you reach Santa Barbara, a charming small city with many historical sites and charms, plus great restaurants and stylish hotels. People from LA drive up to Santa Barbara to escape for the weekend, as it's very romantic. The Spanish Mission there is one of the most famous, and largest of these facilities that helped settle California in the early 1800's.
In short, you can buzz down I-5 from San Francisco in 6 or 8 hours and not see a thing, or take a day or two more and drive down Highway 1 and see the real California. I strongly suggest you get a good California travel book from Fodor's or some other reputable tour book and start researching what you may be interested in seeing along the way.