Where are you flying from? Does it make sense to fly to Seattle instead of one of your other destinations?
How big a drop off fee will you have on your rental car?
What month are you taking your trip?
The Sequoias are in Yosemite. The Coast Redwoods are within 50 miles of the coast of California.
My style of travel is to take Amtrak to a place I want to go to and then take a rental car on a loop trip and then leave on Amtrak for the next destination and renting again. To get to Louisville or Mt. Rushmore you should fly.

If you have any choice at all, flying into Seattle makes no sense as a starting point for the places you want to visit.

Is there some reason you are going that way??

Washington and the Oregon coast were also part of the sights we wanted to see and figured that could be done just driving through, I suppose. Where would you recommend we fly into?

We are traveling in July and as far as rental drop fee it's already figured into our cost is a non issue. However a train does not sound like a bad idead either

Seattle, any of the Washington coast, any of the Oregon coast, the redwoods, Yosemite and the Grand Canyon would totally fill two weeks if you stop anywhere at all. Maybe you could also squeeze in a couple of the southern Utah parks - but that would be a very fast pace.

That plus Yellowstone, Colorado, Mt Rushmore and Kentucky - just not doable in 2 weeks.

BTW in your OP did you actually mean >>Grand Canyon/Yellowstone and back up through Utah, over to Colorado<< in that order? Maybe checking a map is in order.

oh meant to add -- you can really do the Oregon coast just 'driving through'. The coasts (WA, OR, or N. CA) aren't 'on the way' to the other places you want to visit and would require a major detour.

>>However a train does not sound like a bad idead either<<

Trains are OK - but there are no routes that would get you to all the places on your list. (or even most of them).

Taking two weeks to drive across the northern US and down to Kentucky (maybe Glacier, Yellowstone, Grand Teton, Mt Rushmore, etc.) would be doable. But not down the west coast/Yosemite/Grand Canyon/Utah/Colorado/Yellowstone/Mt Rushmore . . . and so on.

You still didn't answer where you are starting from. It might make a big difference in what we ask you to cut from the trip.
My preference might not match yours.
My idea would be to fly to Portland (PDX) in the morning (red eye). Rent your car and drive west on US 30 to Astoria and then south as far as Cannon Beach or Seaside. You get a great view of the best the Oregon Coast has to offer at Haystack Rock.
From there drive back north through Astoria over the mouth of the Columbia to see a little of the Washington Coast. Head back east on the Washington side and then cut back past the PDX airport to get on I-84 east to Multnomah Falls.
After seeing the falls head back to the airport to turn in the rental car. Take the Red line TriMet from PDX into downtown Portland. Spend a day in Portland and then get on the Amtrak Empire Builder from Portland to Williston ND. Spend the night in Williston before renting a car to go south to Rapid City and Mt. Rushmore. From there, it is your choice as to whether to keep the rental car and pay the drop off or go back to Williston and turn it in before taking the Empire Builder father east-maybe Minneapolis-St. Paul. Fly from there to your Kentucky festival.
You can easily spend another two week vacation and not see the other things on your list.