Is it possible to apply to to two schools under a non binding Early Action plan?

There are restrictions: https://admission.stanford.edu/application/decision_process/restrictive.html

Specifically, when applying to Stanford EA, they expect you not to apply EA to other private schools.

Yale is similar: https://admissions.yale.edu/single-choice-early-action

Basically, you can apply to only one of Stanford or Yale EA, and doing so also restricts you from applying EA to other private schools, or ED anywhere.