Note: I have not seen every episode of King of the Hill. Hank doesn't have Aesop Amnesia. Luanne's flanderization also has an in-universe justification: brain damage sustained in the Mega-lo Mart explosion. As for the veterans, it's obvious they aren't in top form mentally. Dale knows about the affair, but says nothing because he's incapable of producing children. Gerald Goode is another of Cotton's illegitimate sons.
Lizbeth. Age: 21.
From the very first episode we are made aware John Redcorn is Joseph's real father.
Blakely. Age: 27.
King of the Hill
Hank was not always the honest propane salesman or great football player we knew him as. However, they treat Hank quite differently. The final threat being that if she screwed up there, she'd be sent to her grandmother's in Laos. Unfortunately, being older, he never actually goes to Kahn's house and wanders off to party. On top of that, Topsy does have some similarities to Beavis.