I would concur with @mashinations that the schools of architecture themselves are the best source for the information you seek.
Many schools of architecture offer in person information sessions for prospective students and their families. These are separate from the university’s general info sessions.
They may not be willing or able to share specific admission rate statistics but they will be able to talk about what they’re looking for in portfolios and essays.
Schools of architecture are well aware that their BArch programs have inordinately high drop out rates. They want to admit students who understand (as much as it is possible for a high school student) what an intensive architecture education will entail. To that end the admissions team is usually quite generous with their time and information.
Except for Miami, all of the schools on your son’s list look a bit reachy to me (though I don’t have any more hard facts than you do). I would think that your StateU BArch would be a good starting point for a less selective option. Or a local BS/BA+MArch if the BArch isn’t available.
Some BS/BA+MArch programs that are less selective than UVA and UMich (and WUSTL which is in the same league)would be Roger Williams, Clemson and Cincinnati. BA/BS graduates can stay at the same school for their MArch or go on to an MArch anywhere.