Personal pronouns replace a noun antecedent, and their relationship to that noun should be clear. My grandfather was a wonderful storyteller. Whenever he began a story, a crowd would gather around him. My grandparents were a devoted couple. They were married for fifty five years and they died within two days of each other.
Pronoun reference weakens when sentences include multiple potential antecedents.
My grandparents once took my mother and her sisters on a vacation in Las Vegas. They still talk about it. Just break it into bits. Rather they summarize an idea introduced earlier in a sentence or a paragraph. The demonstratives help us to avoid needless repetition, but their reference also must be clear.