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, while the third pig farmer is identified as Avery in "Imbroglio". Avril appears to nominally be their leader , and their interactions suggest that the farmers 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".
In "Drygulch", Benjy and the farmers approach the Little Daisy garage with guns openly displayed. After Viktor notes their approach and turns off the lights in the garage, Benjy asks whether the farmers have been seen, but Avril replies that he does not care. Benjy and the farmers break into the garage and engage Viktor in a firefight in "Myopia". Their confrontation is interrupted by the arrival of Rocky and Zib via the trapdoor in "Blindside"; the distraction enables them to injure Viktor and proceed into Lackadaisy. In "Malarkey", the pig farmers enter Lackadaisy proper and shoot at the bar while Mitzi, Rocky, Freckle and Zib hide behind a craps table. Avril plans to burn Lackadaisy down in "Skedaddle", but is distracted when Rocky and the others break cover and run for the storeroom.
In "Deadlock" the pig farmers enter the caverns and split up while searching for the Lackadaisy crew; Avery takes the passage leading to the storeroom. He confronts the Lackadaisy crew in "Doolally", but is shot and quite possibly killed by Freckle before he can open fire, who takes his tommy gun.