Pointing to a lady,a girl said,"She is the daughter-in-law of the grandmother of my father's only son." How is the lady related to the girl?

$A$ is the father of $X$; $B$ is the mother of $Y$. The sister of $X$ and $Z$ is $Y$. Which of the following statements is definitely not true?

$A \div B$ means $A$ is the father of $B$,$A - B$ means $A$ is the wife of $B$,$A \times B$ means $A$ is the brother of $B$,$A + B$ means $A$ is the daughter of $B$.
If $P \times R \div Q$,which of the following statements is true?

Pointing to a boy,Seema said,"He is the son of my grandfather's only child". How is the boy related to Seema?

$A$ is the father of $C$. But $C$ is not his son. $E$ is the daughter of $C$. $F$ is the spouse of $A$. $B$ is the brother of $C$. $D$ is the son of $B$. $G$ is the spouse of $B$. $H$ is the father of $G$. Who is the grandmother of $D$?

To find out the answer to the above question,which of the statements can be dispensed with?