Penny has a sister, she helped with her melted crayon bikini wax mentioned the the parking spot ep.
Is that the same sister who shot her husband when they were both drunk?
Iirc, Sheldon has an uncle they call “Stumpy”.
Some male member of Sheldon’s family had a run in with a badger. I don’t recall the details.
From season 4 episode 2, “The Cruciferous Vegetable Amplification.”
ftg
26
Again, the TBBT wiki has all these details and more. E.g., here is the entry for Sheldon’s family.
Leonard’s younger brother is Michael.
Missy is now married and had a baby in one episode. Her current last name, that of her husband or Sheldon’s niece/nephew is unknown.
Etc.