I guess many people do a two week road trip around Yellowstone/Grand Tetons and many do two weeks in Pacific Northwest so it’s not impossible. Few thoughts -
Depending on routes you are looking at 12-15 hours driving between say the top of Yellowstone to North Cascades/Seattle or from Jackson to the Oregon Coast. So that’s effectively two days of your holiday and if you want to break up the journey more and/or spend a couple of days en route then that becomes 3-4 days.
Where are you thinking of flying in/out of? Jackson Hole or Bozeman require a connection or somewhere like Denver or Salt Lake City are a long drive to Grand Tetons/Yellowstone and again if you wanted to catch a few sights on the way that’s another couple of days. It doesn’t rule it out but it’s just worth thinking about.
It might be worth considering a loop from either Denver or SLC that adds in sights in Colorado or Utah or adding in Glacier National Park.
One way car hire isn’t impossible but worth double checking that hire outlets at smaller airports like Jackson Hole are willing to do as that might affect your decisions on where to fly to.
We did 17 days - including travel days - in Washington and Oregon and didn’t fit in everything we wanted. You could easily spend three-four weeks there. So we did -
Seattle, Mt Rainier NP, Mt Hood, Portland, Oregon coast (Staying in Yachats but visiting Cape Perpetua and the dunes near Florence), Cannon Beach (didn’t stay there but spend the day on the beach) Astoria and Olympic National Park.
We wanted to do the San Juan islands but couldn’t manage it without it all being a rush.
If you added in the islands, North Cascades, Columbia River Gorge, some Oregon wine tasting and even headed further south to do Crater Lake and even the Redwoods in Northern California that’s easily a month.
I guess everyone is different but my ideal month would be three weeks road trip and 5 days - a week chilling somewhere, beach or nice hotel with a pool or on a Dude Ranch if you end up doing Wyoming.
Enjoy the planning and let us know what you decide!