second wife sons and daughter

Whether the property was demarcated / partitioned between your father and his brother before sale or not ? 

What is the relevance of your father's second marriage and children from this marriage qua sale of 5 acre land by brother of your father ?

Confusing and vague information can not lead to form proper opinion and oblige.

The facts as posted lack clarity? What is the relevance of your father's second marriage? Why you want a share from the property held by the brothers of your father? Please post simple but complete facts bringing out the real issue, if any.