Although it is said here that Seth Hazlitt's brother Richard, his nephew Mark and his niece Carolyn are his only relatives, he is later shown to have several cousins who live on a plantation down south in Dixie.
In this episode, it's revealed that Richard is Seth's only living immediate relative. In later episodes it is explained that Seth has a daughter and granddaughter and he also has a niece who visits Cabot Cove in the last Cabot Cove episode of the series.
Larry Linville's second appearance in Murder, She Wrote. He was also in the episode "Murder takes the bus", playing a different character.