Buying a property

I am in the process of buying a property. This is property was inherited to the seller from his father. However, i am facing an issue from the kid of the seller, who was given for adoption by the seller. The kid who went for adoption claiming that it is not his father own/self earned property but was inherited from his grand father as such he too have equal rights thus the sale/agreement of sale will be void without his consent. The seller confirmed that there is no will by his father nor he wrote any Will. He got two sons and one daughter and property is still undivided and there is no Will. The seller got his share of property after death of his father. Seller and two of his brothers shared the father property in a equal shares as such there is no issues from his brother side. 1) Is claim by the kid, who was given for adoption by the seller, is legally tenable 2) What is the difference if there is a Will and no Will and will it make a difference if seller dies during the process? 3) Can seller brothers have any claim? 4) Is there a timeline that one file a case against the buyer? 5) Any other points to be considered before proceeding further?