The football players tend to cluster into Film, Theatre, and Television (FTT) majors, or at least they did when I was there.
And yes, Michigan is somewhat easier to get into than ND because of its size and public orientation, but again, it's a fantastic school.
Notre Dame in terms of academic profile and results for graduates is very similar to the lower tier Ivies of Dartmouth, Cornell, and Brown. Columbia is like a half-step up, Harvard a full step.
But about the anecdote with your cousin. I've heard lots of stories of, say, Yale hockey players with like a 23 on their ACT. Compared to ND football an Ivy League hockey program is an absolute fart in terms of revenue, fanbase, anything, but they're willing to cut those kinds of corners.
For that reason one of me and my friend's first impulses was that Brandyn must have been ridiculously lazy academically - like he didn't show up to English class for three months or something like that. The bar to get these guys in academically, we thought, has gotta be so absurdly low. But the serious interest from Michigan seems to be indicating it may be an ND specific problem. I don't know.