My son went to a boarding school like you are describing. Basically the top third of the class went to T10 schools. Then the second third went to amazing schools. There were even a few students in the bottom third who ended up at Ivies. There is a lot going on behind the scenes, especially at boarding schools.
In my son’s graduating class, there were 15 kids who matriculated at Princeton. The boarding schools have spent years cultivating relationships with top colleges. There is a kid who I know from my son’s HS who was waitlisted at UChicago, but then a college counselor picked up the phone and called the admissions office. Was able to convince them to convert the waitlist to a Z-list (one year deferral admit). All of this is just a way of saying that the college counselors at the top boarding schools wield enormous influence. Much more than can be conveyed by GPA and scores alone.
But the GPA is typically the first pass. Top 10% is fine. Top 1-2% would be better, but I suspect that you’ll get a decent look at any of the schools on your list. Your best chance obviously would be at Duke. Columbia is a lot more risky, because you have no connections there. Look at the scatterplots to see how many students in past years from your HS have been accepted/waitlisted.
Your ECs look good. Depends on how you frame things, and how your college counselor writes about them in the letter. Running a activist organization sounds like a big deal. But it depends what the organization is, and how well recognized it was. David Hogg for example was notably rejected from Harvard originally, and then took a gap year building up the March for our Lives organization. He was scooped up by Harvard in the early round the year after. So for anonymity’s sake I’m sure you want to keep things private. But does your activist work rise to the level of David Hogg?