Sale Agreement

My father has a ancestral property registered under my deceased grandparents name. My father is one of their 5 living children.This ancestral property is under my fathers possession only. Through the registered will of my grandmother, my father has right over 50%(+the remaining share of his deceased mother and his share along with the share from his fathers portion). Out of 5 one of the sibling do not agree to the terms of the will and wants to have equal division. We have received an offer to buy my father's share(as per the registered will) at 22% amount payable at the time of agreement. My question are,can my father enter in such agreement to sell off his share? if yes, what are the ways for him to safeguard his interest during his sale? since the broker in infamous to delay the agreement.We are familiar and will put time bound clause but what are some strong clause that may stop the broker to delay or try to negotiate the terms of sale at a later stage. There is no property dispute case in the court as of yet.