Unless you plan on driving while the other sleeps, doing anything other than i5 all the way would be exhausting. Just made the same trip in July and we stopped in Redding, CA to break the drive up into 2 days ~9 hours driving each.

I’d recommend sight seeing once you get here. After spending some time in Seattle, take a ferry across the puget sound to Bainbridge and then take hwy 101 all the way around the peninsula. It loops around the olympic mountains and takes you past all the sights. That’s about 6 hours of driving so you’ll probably want to split that into a few days if you can.

You’ll definitely have to check weather and road conditions for the peninsula which should be easy to find online.

Good luck and safe travels!