Good choice to rent the car, for motels I like Best Western (many serve breakfast) and Super 8. Hampton Inn is also good and serves hot breakfast.

<Chains are not allowed on rental cars and use of them will void the insurance.>

I did not know that. The OP will have to watch the weather very carefully then. I would think the rental companies would allow chains, as sliding into another car, or off a cliff would cause a lot more damage to the car and occupants. They will just have familiarize themselves with the roads and have alternate routes in mind.

For Yosemite, one can park in Midpines park and ride or maybe at one of the motels in El Portal and take a YARTS bus into Yosemite Valley. Chains are seldom needed that far along hwy 140. The main altitude rise/more snow typically is after El Portal.

Here are the chain requirements for Yosemite:

http://www.nps.gov/yose/planyourvisit/chains.htm

They can meet this by renting a small SUV such as a RAV4. These are equipped with m/s tires that meet all but the " no exceptions" category of chain control, which is very unlikely to occur in March, especially on the western approach road ( El Portalmentrance). They will still need to carry chains in the car--- buy at one of the dealers that allows free return of unused chains.

Book your lodging inside the parks at Yosemite and Grand Canyon. Be sure to use an "official " website, not a third party.

Www.yosemitepark.com

Www.grandcanyonlodges.com

The kids might like the Curry Village experience at Yosemite. Be sure and get a heated cabin!

For motel chains, we prefer Beat Western. Most do include full breakfast with the room,'or at least a heavy " continental" breakfast with lots of choices.

Good choice to rent the car. I can't imagine trying to navigate traffic in LA, driving a camper. Not for the faint hearted!

Decide more on your itinerary, and we can recommend places to stay.

A low-priced brand we like is Holiday Inn Express, which usually offers free parking, free wi-fi and complimentary hot breakfast.

There is nothing wrong with a round trip. Going from Las Vegas to Yosemite and then SF and then going down the coast back to LA for departure does not constitute back-tracking. I would decide on RT or open jaw based on the price of the flight and then plan the itinerary accordingly.

"Las Vegas to Yosemite and then SF and then going down the coast back to LA for departure"

How is that RT? Arriving LV and departing LA.

Remember to factor in the price of a rental car drop fee, if you are leaving from a different airport than you got your car.

I assumed that the arrival point in the U.S. was still L.A. I meant from LA to LV and the Grand Canyon (or the GCNP and other national parks in southern Utah before LV).

" We fly in and out of LA"

As a fellow brit who has visited California twice I would suggest that you don't try to do too much in one visit. Our first visit took in San Francisco, Yosemite, Sequoia, Monterey then down the coast via Hearst Castle, Solvang, Los Angeles, San Diego and even crossed into Mexico and I agree you really dont want to go to Tijuana. We then went to Vegas, Grand Canyon and finally New york for a couple of days on the way back. This was a great trip but very tiring. The second trip we again went to San francisco then onto Lake Tahoe, Sacramento, back to San Fran then internal flight to San Diego which is our favorite city and returned home fron Los Angeles. Had we known that we would be going twice we would have done San Fran, Yosemite, Lake Tahoe, Sacramento on one trip and Los Angeles, San Diego, Las Vegas and the Grand Canyon and added Bryce and Zion on the other trip. If you are definitely only going once then go with your plan but if you can possibly go again then consider reducing your schedule.