Yale and Stanford.
Stanford’s allows you to apply to multiple schools EA, let me refresh my memory on Yale’s policy-
https://admissions.yale.edu/single-choice-early-action
“Single choice” for Yale – exceptions noted on the website.
It looks like Yale only allows other schools to be applied to under regular decision. So no, I don’t think you could do Stanford and Yale early. Yale’s policy was a little complicated- someone correct me if I interpreted it wrong!
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.
Read the rules of the two schools carefully. It can all be found online.
Most universities with EA options allow students to apply to other school EA without any restrictions. That includes Chicago, Georgetown (restricts applicants from applying ED elsewhere though), MIT, Michigan etc…
Harvard, Stanford, Princeton and Yale all have restricted Early Action. If you choose to apply EA to one of those, you cannot apply EA or ED anywhere else, unless it is public. So you may apply to any of those four EA, and also apply to the University of Michigan and/or the University of Virginia EA as well.