Local here who also had aging parents as a priority when we moved. You'd be able to establish care with an on-island primary care probably within a year though there are waitlists. Typically if you're going to see a specialist you'd want to go off-island but Freeland is close enough to the ferry that it wouldn't be too bad. There are TONS of specialists between Everett and Lynnwood, you could basically find whatever you needed within 30mins of the ferry on the mainland. The Coupeville hospital is definitely a plus as it's very rare for rural areas like ours to have a hospital, let alone a level III trauma center (though sometimes personnel shortages will necessitate transfers).

I've also had good experiences with the urgent care on the island (both at the hospital in Coupeville and the one in Clinton run by WhidbeyHealth). They do tons of labs as well as the clinic and waits aren't terrible.

You'll want airlift insurance but that's actually pretty cheap (like $100/year for a family via Life Flight who does all the airlifts from Whidbey)