Road trip Los Angeles to Seattle

Do you understand that August is the peak holiday month in the US. Is it essential that you go then ... 10-26 September would be so much better.

But with 15 nights, I would look at San Francisco (3 nights), Yosemite NP (2 - if you can find accomm), and Portland (2). The outstanding features for me are Yosemite NP, the redwood state parks (Humboldt SP and Jedediah Smith SP), Crater Lake NP, Mount Hood, Mt Rainier, and the Columbia River Gorge.

You can cover the distance okay with seven days travel and 4-5 hours per day actually driving. Look at the lower-end Wyndham Group motel chains - Super8, Days Inn, Comfort Inn, etc. They have a good online booking system.

Thank you! Yes we do know that this is the peak time, but we can't do otherwise as college starts on the 25th of August...

Then you will have to spend a lot of time searching for accommodation, starting with Yosemite NP, and its nearby towns.

Alright! Thanks! So would it be wise to find accommodation in a nearby town, then in the morning head to the park with a shuttle and do a trail such as the Yosemite Valley loop ? then go back to the hotel and go on with our itinerary the next day ?

What's your interests for this trip, mountains-coast-desert, small-big cities, wineries, food or just road tripping?

How much time in LA will you spend, Disneyland, Hollywood, Museums?

I think with 15 days and only wanting to drive 4-5 hours per day that you may need to cut something. Either do Seattle to SF as suggested by #1 plus Yosemite if you can get lodging inside the park or in nearby El Portal, or else SF to LA plus Yosemite.

We are interested in mountains, coast, and road tripping.
Spending 4 nights in LA is enough right ? To get a feel of the place ahaha. defo not Disneyland but Hollywood and all yeah!

Thank you for your advice ! our provisional itinerary would be : LA-Yosemite-(Someplace)-San francisco-(someplace between SF and PL)-Portland-Seattle.

What do you want to see-do in LA, 4 nights is a lot unless you have certain things to do. It's a massive suburb, goes on forever so a rental car would help.
Be prepared for major traffic at all times, slow going.

If you go with 4 nights in LA that leaves you 12 to drive all the way to Seattle via Yosemite and SF, lots of driving, too much IMO. Easy to get by with 3.

Consider LA to SF only or SF to Seattle so you can enjoy the trip, explore a bit more and have more fun versus sitting in a car the whole time.

You could try something like this, nice variety. Has everything on your list and is doable but still moving.
3 Nights - LA
2 N - Mammoth Lakes, Hwy.395 has stunning scenery, high desert and cool mountains. Mammoth offers lots of things to do, beautiful area.
You could go up the coast which would still be 2 nights lodging but you'll get plenty of awesome coast line north of SF, you don't have much time.

2 N - Yosemite Valley via Tioga Pass. Probably have to stay in El Portal. Keep trying for a cancellation in the Valley. Could also try the http://yosemitebug.com/ Good luck and keep trying!
3 N - SF
1 N - Humboldt Redwoods
1 N - Crescent City for Jedediah Smith Redwood, hike-walk Stout Grove-easy walk.
1 N - Chemult OR via Crater Lake
2 N - Portland via The Dalles
1 N - Seattle