Pointing to a man on the stage,Rita said,"He is the brother of the daughter of the wife of my husband." How is the man on the stage related to Rita?

$P$ is the brother of $Q$ and $R$. $S$ is $R$'s mother. $T$ is $P$'s father. Which of the following statements cannot be definitely true?

There is a family of six persons $A, B, C, D, E$ and $F$. They are Lawyer,Doctor,Teacher,Salesman,Engineer and Accountant. There are two married couples in the family. $D$,the Salesman,is married to the Lady Teacher. The Doctor is married to the Lawyer. $F$,the Accountant,is the son of $B$ and brother of $E$. $C$,the Lawyer,is the daughter-in-law of $A$. $E$ is the unmarried Engineer. $A$ is the grandmother of $F$. Which of the following is one of the couples?

$I.$ $A, B, C, D, E$ and $F$ are six members of a family.
$II.$ One couple has parents and their children in the family.
$III.$ $A$ is the son of $C$ and $E$ is the daughter of $A$.
$IV.$ $D$ is the daughter of $F$ who is the mother of $E$.
How many female members are there in the family?

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

$A$ and $B$ are brothers. $C$ and $D$ are sisters. $A$'s son is $D$'s brother. How is $B$ related to $C$?