$X$ told $Y$,"Though $I$ am the son of your father,you are not my brother". How is $X$ related to $Y$?

In a village of Bastar district in Madhya Pradesh,only two types of people live who belong to a tribal class. The first type is known as class $A$,while the other is known as class $B$. In that village,there is no other type of person except these two. The activities of both types of people are governed by perfectly patterned norms of social behaviour. Each person of the tribe has to obey the norms. They are rigid about this.
As far as marriage is concerned,the following norms are to be followed:
$(A)$ The people of class $A$ cannot marry any other member of their own class,though they can marry members of class $B$.
$(B)$ After being married,each male member ceases to be a member of that class in which he was born but automatically,he becomes the member of the other class to which his wife belongs.
$(C)$ As far as females are concerned,they remain the members of their own class after being married.
$(D)$ On his birth,the child automatically becomes the member of his mother's class.
$(E)$ When any male member becomes a widower or divorcee,then he again belongs to the group in which he was born.
$(F)$ Nobody can marry more than one person according to social laws.
Any class $B$ female can have:
$(P)$ Grandfather born in class $A$
$(Q)$ Grandmother born in class $A$

$A + B$ 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 $B$; $A \div B$ means $A$ is the daughter of $B$. If $P \times R + Q$,which of the following is true?

Pointing to a gentleman,Deepak said,"His only brother is the father of my daughter's father." How is the gentleman related to Deepak?

$Q's$ mother is the sister of $P$ and the daughter of $M$. $S$ is the daughter of $P$ and the sister of $T$. How is $M$ related to $T$?

$A, B, C, D, E, F$ and $G$ are members of a family consisting of four adults and three children. Two of the children,$F$ and $G$,are girls. $A$ and $D$ are brothers and $A$ is a doctor. $E$ is an engineer married to one of the brothers and has two children. $B$ is married to $D$ and $G$ is their child. $A$ is the son of $C$. Who is $C$?