You've omitted all travel time - What you actually have is:

7-10 Dec - Disneyland
11-12 Dec - San Diego
13 Dec - Phoenix
14-15 Dec - Grand Canyon
16 Dec - Hoover Dam and Las Vegas
17-18 Dec - Yosemite or Death Valley
19-21 Dec - San Francisco
22-26 Dec - Leavenworth or aspen

Couple of quick comments re issues I see.

4 days is a long time for Disneyland (and this is from someone who loves DL). Two full days should be plenty.

Driving LV to Yosemite will take FOREVER - it is between 9 and 10 hours straight w/o any stops. And most of it is a butt ugly route.

You can't get from Las Vegas to Yosemite in the dead of winter. Tioga Pass will be closed. The only way is go all the around the Sierras and take Highway 99.

Is there a reason for Phoenix?
The comment about Tioga is correct--you would need to enter from the western side--a LONG way from LV
Aspen is a LONG way from SF. Leavenworth? Don't know where except Kansas, but I haven't looked.
Disneyland is expensive and 2 days is plenty, as said.
Death Valley is interesting in desert sort of way
Are you flying open jaw?

The Leavenworth referred to is in Washington which is a magical place at Christmas. Flying to Seattle and renting a car there is the best way to get there.
Plan on coming back to the US sometime in the summer to get the most out of your first trip to Yosemite.
Aspen is too far to try for. There are many places to ski on the west coast without going to Colorado.

Tahoe would get you a white Christmas and skiing and is much closer to San Francisco then Leavenworth or Aspen. Or you can drive back down to LA from SF and fly in and out of LA pretty much anywhere (Aspen, Park City, Jackson Hole, Taos, Vail), we like Park City. I've listed internal flights between cities to give you more time.
But you can also drive the whole circuit. LA/Disneyland - San Diego - Vegas - Grand Canyon - San Francisco - Tahoe - LA. Adds more time but introduces possiblity of road trip adventures.

I would probably skip Phoenix and structure as follows:

(Pick up car in LA and return in San Diego)
7-10 Dec - Disneyland/Beaches/LA
11 -12 Dec - San Diego
(Fly San Diego to Vegas)
(pick up car in Vegas or take a combined tour to Hoover Dam and Grand Canyon)
13 - 14 Dec - Las Vegas/Hoover Dam
15 - 17 Dec - Grand Canyon/ Las Vegas
(Fly Vegas to San Francisco)
18-21 Dec - San Francisco
(Pick up car, drive to Tahoe)
22-26 Dec - Tahoe
27-28 Dec - Drive to LA/Fly home

I think POIson has given you a terrific itinerary, however, know that you cannot count on snow in Tahoe at Christmas. Snow is a sure thing in Tahoe only after the middle of January. We've skiied in mud in December and we've had great snow other times. Also, if you do drive to Tahoe, you have to do it when the roads are clear -- if there's a hint of snow, the highway patrol will impose chain controls (and yes, they do check), and most rental car companies do not permit chains to be used on their cars.

>>You can't get from Las Vegas to Yosemite in the dead of winter.<<

You can

But >>The only way is go all the around the Sierras and take Highway 99.<<

That is what I meant by 9-10 hours of butt ugly . . .

I also agree with dropping Phoenix.
Lots of folks from Australia love to spend many days at Disneyland, in fact there is a long thread over on TA with folks complaining because Disney did away with the 14 day pass for this year.
Couple of good outlet malls in Las Vegas if you are into shopping.
Grand Canyon might have snow, might not.
Have a great trip.

I'm guessing Phoenix was an overnight stop on the way from San Diego to the Grand Canyon. I'd cut back LA by a day and add that day to San Diego.

San Francisco/Yosemite are the real outliers unless you fly there from Las Vegas. Death Valley instead of Yosemite works great, but you still have to get to San Francisco.

You could find a ski resort near Salt Lake City instead of going to Colorado or Washington.