She is the paternal aunt of Meg, Chris and Stewie and sister-in-law of Lois.

Karen 'Heavy Flo' Griffin (voiced by Kate McKinnon) – Peter's older sister, who first appears in ' Peter's Sister'.

Chip Griffin (voiced by Seth MacFarlane) – Peter's vestigial twin brother, who appears in ' Vestigial Peter'.

In ' Mom's the Word', it is revealed that Thelma has died of a stroke. Thelma Griffin (voiced by Florence Stanley in the first appearance, Phyllis Diller in later appearances, Alex Borstein as a young woman in 'Don't Be a Dickens at Christmas') – Ex-wife to Francis, mother of Peter, and paternal grandmother of Meg, Chris, and Stewie.

Peter travels to meet him after he learns that Francis, who had just died, was not his biological father. He lives in Ireland and is regarded as the town drunk (a highly respected position) in his neighborhood. Mickey McFinnigan (voiced by Seth MacFarlane) – Peter's biological father, and the biological paternal grandfather of Meg, Chris, and Stewie, and father-in-law of Lois.In ' Peter's Two Dads', Francis attends Meg's 17th birthday party, and is crushed by a drunk Peter while attempting a unicycle trick to entertain the party guests as 'Pee-Pants the Inebriated Hobo Clown.' The injuries prove fatal, and as Francis is dying in the hospital, his last words to Peter before his death are, 'Peter… you're a fat, stinking drunk.' An obsessively devout Roman Catholic, he hates Lois because she is not a Catholic, and often calls her a ' Protestant whore', disapproves of his son's family's lifestyle, and frequently attempts to force his religious views on them. He was once married to Peter's biological mother Thelma Griffin.

Francis Griffin (voiced by Charles Durning) – Peter's grumpy, stubborn and abusive 82-year-old adoptive father, Lois's adoptive father-in-law, and the adoptive paternal grandfather of Meg, Chris, and Stewie.The characters listed below are the extended family of the Griffin family that come from either Peter's side of the family, Lois's side of the family, and the occasional members of Brian's family: Brian Griffin (voiced by Seth MacFarlane) is the family's 6-year-old anthropomorphic talking white Labrador Retriever and the best friend of both Stewie and his father Peter.

Biscuit bitch