I think we really need to avoid to "frat" label. It leads to all sorts of confusion, especially as the Race has cast two different teams that had a relationship of being fraternity brothers in college.
"Frats" is being used for teams some perceived as looking like a stereotype, and this has been done on more than one team in more than one other season in addition to the two Races where the label was factually accurate and appropriate. FWIW, "preppy" is just an accurate a label as to a stereotype appearance but without the TAR baggage.
The younger set of brothers this season -- we know that one of them is in a fraternity at Georgia Tech, but we don't know that is the case with the other brother.
Just my teo cents worth.