The pig farmers are three bootleggers whom Rocky encounters in "Rumrunner". Based on dialog it is clear that they have had prior run-ins. In "Hydrophoby" one of the farmers is identified as Avril. In "Sunshine" another one of the farmers is addressed as Emery. Avril appears to nominally be their leader , and their interactions suggest that they are related.
In the comic
After confronting Rocky in "Rumrunner", the farmers abduct him in "Hydrophoby" and place him in the back of their truck with "Frothy", a rabid pig that Avril was forced to shoot. In "Crack-Track" the farmers intend to kill Rocky by pinning him to a set of railroad tracks with nails through his tie, but he escapes in "Face-plant".
In "Scathefire" through "Schadenfreude", Rocky and Freckle visit and ultimately destroy the farm where the pig farmers live and work. The farmers discuss the attack and how to respond in "Lambaste", with Avril noting that "some people" owe them a favor.
It is revealed in "Muckamuck" that, shortly prior to the timeframe of the comic, the pig farmers received a large sack from Mordecai, Nico and Serafine and presumably fed the contents to the farmers' pigs. In the present, Avril tells Emery to get Benjy Jessup and Jessup's truck, presumably as part of Avril's plan to deal with Rocky.
During "Vaudevillian", Avril meets with Asa and Mordecai in Asa's office. After Avril describes the destruction of the pig farm by Rocky, and points out that Marigold has been using the farm to dispose of bodies but has not paid the farmers, Asa agrees to lend them, "some very indirect assistance".