What do you mean by "My mother sold one allotted plot of an unregistered and unapproved layout society in her relatives"?
Is it that your mother had sold plot to relatives? How is the purchaser related to her?
What are the contents of the agreement? Is sale consideration (price) mentioned there?
What is the relevance of "unregistered and unapproved layout society"? Please post clear facts?
Obviously, the land belongs to her? How is it that you are having a claim over it?
How is that mother is the owner of the plot - by purchase or by inheritance?