Son graduated from top public where >25% of the kids went on to IVYs every year. Loads of multiple early applications and admits to the same schools. Take away from that would be that if you have what Yale is looking for, they’d be happy to get you both.
Despite any similarity in stats, interests and school, where you really get to differentiate yourself is in your essays. One hint: more than most schools, Yale really loves kids who want to explore everything! The kids with the HS STEM background who can’t wait to get into a comp lit seminar… The kid with the history/writing awards who is deeply intrigued by organic chemistry and wants to sing with the 'Poofs, etc. The take around here is often that kids need to have a shining focus on one interest. That isn’t the case it Yale. They like to see stellar achievements in a core area, but beyond that, they like renaissance kids with broad interests. Don’t be afraid to share your goals and interests in your essays.
None of us knows exactly what goes on in Yale’s (or any other) admission room and it is futile to guess. My best advice is for everyone to apply where they want when they want (be it REA, RD etc.), have each candidate put forth the best application possible, and let the chips fall where they may.
Recognize that Yale is a big reach for any unhooked candidate. Each applicant should develop an application list that includes reach as well as match and safety schools that appear affordable (per Net Price Calculator) and that they would be happy to attend.
Last year the Val and Sal of my sons school were both accepted. One was deferred and then accepted and the other accepted regular decision. 2 kids very similar in academics. Some of the same clubs but totally different interests. Before that we have no idea if and when anyone from our school was ever accepted to Yale.