Who is Aphrodite Venus grandmother?

It depends upon which genealogy of Aphrodite's birth you "believe":

Ouranos (at castration) and Thalassa (sea): Aphrodite's grandparents by Ouranos could be Gaea and Aither, Gaea alone, Aither and Hemera, or Nyx; Thalassa's parents would be Aither (Air) and Hemera (Day).

Dione and Zeus: Aphrodite's grandparents would be by Dione - Oceanus and Tethys, Ouranos and Gaea, or Aither and Gaea; and by Zeus Rhea and Kronos.

Or the rarer Hemera and Ouranos; by Ouranos could be Gaea and Aither, Gaea alone, Aither and Hemera, or Nyx;by Hemera her grandparents would be Erebus and Nyx, Khronos and Nyx, or Khaos.