My grandmother is Jajo (Jay-joe) . . . Grandfather, Papo. (Pop-oh)
Great grandparents were Mano and Popo. Great Aunts are Nini and Pito to their grandchildren, and if my siblings and cousins have children, their grandmothers' names will be Dobie, Dinka, and Beebah . . . no clue about the grandfathers' yet. The rule is that "grandparent" cannot be used in any of it's forms, not even in other languages, because as soon as you're a grandparent you're old, and my family does not let our members get old . . . and anyway, everyone calls each other by the nick names anyway, which always originate with a young family member who can't pronounce the names correctly. I'm Didden.
My grandparents on the less nick name oriented side of the family were simply called grandmom and grandad (insert last name). I always thought it was weird they didn't have nicknames.