Final answer:
The author may have chosen these family dynamics to add contrast, highlight challenges faced by the protagonist, and create opportunities for conflict and character development.
Step-by-step explanation:
The author may have chosen to give the Granite Abbeville a mother with typical intelligence of that time and no brothers while giving the antagonist's family to add contrast and highlight the challenges and limitations faced by the protagonist. This choice could serve to deepen the complexity of the story and create opportunities for conflict and character development. For example, the absence of brothers in the Granite Abbeville's family might make her journey more difficult, as she may not have the same support or protection that a brother could provide. On the other hand, by giving the antagonist's family brothers, the author may be highlighting the privilege and advantages they have compared to the protagonist.