Jerry Mackleberry is the twin brother of Larry Mackleberry and the brother to Sherri, Terri and Unnamed. He and Larry attended Sherri and Terri's funeral in "Treehouse of Horror XXVII".
Both Jerry and his brother Larry's existence is non-canon, as their only appearance was in the above-mentioned Treehouse of Horror episode, which are considered non-canon to the regular shows' continuity.