If you're talking about Fahrenheit 451 then they hardly interact with each other. Millie is just self-centered and stubborn.
Mildred, Montag's wife, was the informant on montag's home.
Husband and wife relationship is called a marriage.
There is no relationship. She would simply be your first cousin's wife.
Your cousin's wife is not related to you.
Your wife's nephew is your nephew, but the English language has no relationship term for your nephew's wife. Just call her "my nephew's wife."
At the end of Section 2 in "Fahrenheit 451", Montag's destination is his own home. He arrives home after service call to find his wife, Mildred, overdosed on sleeping pills.
I have a great relationship with my wife.
Your wife's niece is also your niece, and her daughter is your great niece. It is to be hoped that you do not have a relationship WITH her, merely TO her.
Your mother is not related to your wife's mother.
Your mother is not related to your wife's mother.
Your wife's brother is your brother-in-law, but in the English-speaking world the his wife is not related to you. It is common, however, for your children to consider her to be their aunt.
There is no relationship, you do not share a common ancestor.