When terms denoting family relationships are used as proper nouns (as names), they are capitalized. However, when the terms are used as common nouns (not as names), they’re not capitalized. Generally, there will be a possessive pronoun (my, her, his, our) or an article (the, a, an) in front of family titles used as common noun.
It’s easy to get confused about whether you should capitalize family names in your writing. If you come across a family “title” such as mom or dad in your writing, ask yourself: Is this title being used as if it were a person’s name? Is the person being directly addressed?
In the examples above, Mom, Dad, and Grandma are capitalized because they are being used like names. You could replace them with proper names without changing the rest of the sentence.
If a family member is not being directly addressed, but rather is being spoken about, his or her family title should not be capitalized, and an article or possessive pronoun should be used before the title.
When quoting a conversation, simply think about whether that person is being directly addressed in the conversation.
“I feel for Melinda’s loss,” said the neighbor. “Everyone remembers her aunt’s generous nature.”