Lee Ain't Heavy, He's My Brother - S4-E21
Character mistake: Jack's older brother Lee comes for a visit. In the second season when Jack's Uncle visits, both make note of Jack being his only nephew. Lee would be his other nephew.
Suggested correction: Although it's not stated in the show, theoritically speaking, it WOULD be accurate if Jack and Lee were HALF-brothers (with same father since both last names are Tripper) and Fremont was the brother of Jack's mother, then Jack COULD be his only nephew as Lee would have NO relation to Fremont.
I submitted the above correction based on a theory that would make it possible, although in reviewing one of the scenes involving Jack's Uncle, I realise this would not be the specific case. Uncle Fremont most likely is the brother of Jack's father (not mother like the theory) due to the fact when he tells Mr. Roper that Jack's father is happily married but that doesn't stop him from having "fun" with a friendly nudge. He most likely would not say that if it was against his own sister. So yes, the theory didn't apply in this specific situation. Instead, the situation here is during the Roper early seasons, the episode came out with the Uncle and a year or two later (during the Furley era) Lee was intruduced. Neither were ever mentioned in any other episode so it could be simple inconsistent screenwriting.