Isn't Grand Canyon (South Rim) to L.A. at least 10 hours driving, even without possible weather problems?

Yosemite to Vegas is probably also 10 hours driving, how much of these places do they actually expect to have time to see?

Frankly, I'd suggest dropping at least one of these places, even on a "trip of a lifetime." Maybe drop Yosemite or Napa/Sonoma?

Also, I'd consider staying in Morro Bay or San Luis Obispo instead of Santa Barbara.

Without hotel bookings already, Yosemite and Vegas may be challenging those days; the other places, probably possible, but get these two places and Grand Canyon ASAP!

Strongly recommend they buy chains for the rental car AND try putting them on at least once before leaving the SF bay area. Also recommend they not attempt this entire trip without being skilled in driving through snow, or at least be prepared to cut back in case of bad weather.