@iyayard - Your son by all measures seems to have done exceptionally well in terms of admissions at a great set of colleges. Congratulations to your family.
He seems to have had many school choices but for whatever reason you are only rethinking one school he did not choose vs another school he decided to enroll in. However, it is no longer a choice a month later unless admissions at Brown is willing to relook at your application.
It may not be the best thing for your son to be aware that you are so concerned about a wrong choice although most people on CC won’t agree with you that he made a bad choice between choosing one over the other. In fact, I would argue that he might have liked Rice better but it is no longer a choice either. My view is that when the decision has been made, you may focus what you must do for your kid to prepare for NU.
Theoretically, the only choices your son has left is the waitlist school, Duke (does he have more?). If and when he gets off the waitlist, you have a new choice.