From Muppet Wiki

A list of Muppet and human grandmothers and grandfathers, both on screen and in books. In the case of long-running characters, the source listed is the character's first appearance.

The Amazing Mumford

• Grandmum, grandmother -- The Sesame Street Cookbook

Baby Bear

• Grandmama Bear, grandmother -- Episode 3893

Bean Bunny

• Great-great-great-great Grandmother Bunny -- The Tale of the Bunny Picnic

Big Bird

• Granny Bird, grandmother -- Sesame Street

Cookie Monster

• Cookie Monster's Grandma -- Sesame Beginnings

Cotterpin Doozer

• Granny Cantilever, grandmother -- Fraggle Rock

David

• Harriet, grandmother -- Sesame Street, 1976

Elmo

• Elmo's Grandma -- Elmo Gets Homesick
• Elmo's Grandpa -- Elmo Gets Homesick
• Selmo -- great-grandfather, Elmo Gets Homesick

Fozzie Bear

• Fozzie's Grandpa -- Muppet Kids

Gonzo

• Grandma, Show-and-Yell

Grover

• Grover's Grandpa, Wait for Me!
• Granny, Grover Visits His Granny

Herry Monster

• Herry's Granny -- Sesame Street, "Herry's Family Song", Season 17

Athena

• Hoots the Owl, granddaughter -- Sesame Street

Junior Gorg

• Queen Esmerelda, grandmother -- Fraggle Rock

Kermit the Frog

• Great-grandmother Toad -- Kermit's Garden of Verses
• Grandfather Frog -- Kermit's Garden of Verses

King Goshposh

• Granddaddy Whittiner, The Land of Tinkerdee

Mr. Snuffleupagus

• Granny Snuffle -- See You Later, Mashed Potater!

Oscar the Grouch

• Granny Grouch, grandmother -- Sesame Street Episode 0131

Pip and Pop

• Otto and Etta Otter, grandparents -- Bear in the Big Blue House

Rosita

• Rosita's Family -- Sesame Street

Statler

• Statler's Grandson -- The Muppet Show episode 319

Tutter the Mouse

• Grandma Flutter -- Bear in the Big Blue House
• Grandpa Highland McTutter -- Episode 317: The Tutter Family Reunion, Bear in the Big Blue House