grandparent's/grandfather's name ?

[ph2004]

Can I say "my grandparent's name is Peter", or do I have to say "my grandfather's name is Peter" ? Or are both possible ?

 

[Linguist__]

(Not a teacher)

I would say both are possible, but the first is ambiguous, and unless there is a reason to say it, then avoid it and specify which grandparent.