The men work for the county.  They are making a film about food stamps and invade the narrator's home and propety to do so.  The pair treat the family as if they were creatures in a zoo rather than thinking and feeling human beings.  When Granddaddy Cain smashes their camera, they have no choice but to return to their workplace.

Here is an excerpt from the character summaries here at eNotes that should help clarify any confusion.  A link to the page appears below:

‘‘Camera’’ is how the narrator refers to the cameraman who is filming for a county project on food stamps. The camera on his shoulder is so much a part of him that when he hands it to Granddaddy Cain he keeps his shoulder ‘‘high like the camera was still there or needed to be.’’ When Granddaddy deliberately damages the camera, Camera gathers up the pieces and holds them ‘‘like he’s protectin a kitten from the cold.’’