I definitely believe that our loved ones are waiting for us as we cross over, and do want us to be reassured that we won't be alone when we pass.
Not trying to scare you, but is your grandmother in poor health? Sometimes our loved ones come to us just before they pass or just after they pass to let us know not to worry about them, that they are fine, and are safe and secure. I absolutely believe your grandfather will be there for his beloved wife, whenever it is her time to pass.
And no doubt he will be there for your mother when her time comes, too.
Dying folks often talk to their parents, spouses, or siblings; or see them and their deceased children, friends, even pets, as they are close to passing. My own mom saw her mother, my son who died many years ago, Jesus, and many angels.
Love never dies; it continues on in a different plane than where we live now, and we can look forward to seeing our loved ones again.