When writing any genealogical note, commentary, etc. avoid the use of relationship terms without the name of the person attached to it.
"Grandma gave me this picture."
"My Uncle told me where Grandpa was born."
What Grandma? What Uncle? What Grandpa?
You may know to whom you are referring--will someone else?
If you indicate in the first paragraph that you are talking about "Grandma Matilda Johnson," it's not necessary to refer to her using that complete phrase in every sentence that follows. That makes your prose bulky. However, otherwise you should be clear about exactly to whom you are referring.
This is especially true in families where names are used more than once. My mother has three Aunt Ruths. One was always referred to with her last name, one was Ruth, and one was Ruthie.
The point is what is clear to you might not be clear to someone in fifty years.