You can say my grandmother on my mothers side or fathers side. For example: my grandmother on my fathers side is from Scotland, while my grandma on my mothers side is from Peru. You can also say my father's mother is from Scotland and my mother's mother is from Peru.

@MoiraWendy Miller could you explain what are apostrophes?

Maternal or paternal grandfather, or grandfather of my mother's side, or father's side. Please don't forget the apostrophes.