$A$ and $B$ both are children of $C$. If $C$ is the mother of $A$,$A$ is the son of $C$ but $B$ is not the daughter of $C$,how are $A$ and $B$ mutually related?

$I.$ $A, B, C, D, E$ 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?

Anil introduces Rohit as the son of the only brother of his father's wife. How is Rohit related to Anil?

Pointing to a photograph,Vipul said,"She is the daughter of my grandfather's only son." How is Vipul related to the girl in the photograph?

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.
Which of the following marriages is not permissible according to the social laws?

Lakshmi and Meena were Rohan's wives. Shalini is Meena's step-daughter. How is Lakshmi related to Shalini?