When identifying people on pictures, writing about them in your research notes, or asking someone about them, try and avoid only using a relationship to describe the person.
Writing "John's Grandma" on the back of a picture is helpful, but still pretty vague. Who was John and which Grandma is it?
When asking your own Grandma questions, asking her to tell you something about "Grandma" may result in her not talking about who you think she is talking about. Ask her about a specific person--referring to them by name.
When I asked my Grandma questions, I was less confused if I said something like "tell me about your Grandpa--John Trautvetter" instead of asking about "Grandpa Trautvetter." When I asked about "Grandpa Trautvetter" it took me awhile to realize she was talking about her dad who was my dad's Grandpa Trautvetter.
Try and avoid creating more confusing and don't refer to people only by their relationship.