Is the fact that these persons are not clearly labeled and identified a failure on the author's part?

Absolutely not, the story is Granny's..... the other characters could be anyone, as it isn't their story, and they are not the ones walking down memory lane. Granny's passing belongs to her alone. No one else knows what passes through her mind, and the images in her mind may simply be nameless. Our narrator is omniscient, thus, he or she know all, and is imparting Granny's thoughts and feelings as they come. What Granny remembers is important....... but the images are enough.