"Jenna's grandfather" is not an official name.
Jenna's grandfather
Gender Male
Family Mr. Morgan (son)
Jenna Morgan (granddaughter)
Mrs. Morgan (daughter-in-law)
Cartoon debut Jenna's Bedtime Blues (mentioned)

Jenna's grandfather is the paternal grandfather of Jenna Morgan, the father of Mr. Morgan, and the father-in-law of Mrs. Morgan. When his son had bedwetting problems as a child, he helped him get over it the same way his son would eventually do with his own child.