The Crosbys are die-hard capitalists and patriotic Americans. Actually, their patriotism borders on jingoism. They also have a tendency to speak and act toward others in an unreserved manner.
The Mintons are the exact opposite. They are highly reserved people in manner and speech. Horlick Minton is patriotic, but his humanist view means nationality holds no value for him.
The Crosbys are obviously a caricature of a conservative American couple while the Mintons maintain a more liberal core. In this way, we can contrast the two American views. What's fascinating about this foil is that neither couple is whacked with the short end of the foil stick. By the end of the novel, we learn that all four are really good people at heart.