In "Once Upon a Time," what is the relationship between the characters in the story and community in which they live?

The characters in the story live in a terribly divided community, and so this analysis must take place in two parts: one must examine both the family's relationship with their neighbors and their relationship to the people of color who live outside their suburb.
The suburb in which the family lives is understood, particularly in the context of apartheid South Africa, to be both white and afraid of those who are not. Race is a recurring theme throughout the story, no less present for the family's denials of racism:

He was masked; it could not be said if he was black or white, and therefore proved the property owner was no racist.

The family is guided by their fear. They insure against disaster, and in cases in which no such insurance is available, they actively attempt to prevent damage by installing security measures such as alarms, fences, wire coils, and so on. The community of the suburb is homogenous; the actions taken by the family are by no means unique. Gordimer states that: 

The alarm was often answered — it seemed — by other burglar alarms, in other houses, that had been triggered by pet cats or nibbling mice.

Guided by a shared fear and persistent racism, the family is shown to be typical of the community of the suburb.
The community outside the suburb is greatly feared by the family. They are described as rioters, burglars, loafers, hooligans, loiterers; that the story opens with the narrator's fear of being murdered implies that the family is afraid of being killed as well. They are "people of another color," not only living in another part of the city but "quartered" there. The trustworthy ones were made housemaids and gardeners: servants. 
Despite the family's persistent fear of the people from outside the suburb, their housemaid and gardener are very loyal: when their son is caught in the coil, they are described as "the hysterical trusted housemaid and the weeping gardener" while the parents of the child are simply described as "the man" and "the wife." Faced with the death of a child, the maid and gardener, whose own community is somewhat dehumanized over the course of the story, are shown to be more human than the parents of the child.