Squeak and Sofia are set up as natural foils to one another, as are Harpo and the “prizefighter.” Squeak is timid, unassertive, and initially does not stand up for herself when Harpo treats her poorly. Sofia, on the other hand, is quick to fight back against Harpo and leave him when she doesn't approve of his behavior.
In a similar vein, Harpo is possessive and jealous. He wants to own and control Sofia, mostly because he has seen that behavior modeled for him by his father (and other men in his life). The "prizefighter," on the other hand, is not insecure and does not claim unitary ownership over Sofia. He understands that love is not ownership, and that women are not possessions to be bought, sold, or claimed.
Both Squeak and the “prizefighter” are given monikers; Celie rarely refers to them by their real names (Squeak is later referred to by her real name, Mary Agnes, only after multiple women in the story reprimand Harpo for treating her poorly). Their respective characters contrast with those of Harpo and Sofia. The "prizefighter" and Sofia undermine conventional gender roles, while Squeak and Harpo uphold them—at least initially. Through this contrast, Walker provides an alternative set of attitudes and power dynamics that challenge patriarchy, monogamy, and heteronormativity.