Hi
1) Since the land was purchased in your name when you were a minor and that too when your father was alive, the land will belong to you absolutely.
2) Also that the fact that your brother did not challenge the same soon after he reaching 18 years of old or during his entire life time, obviously goes to show that you are the absolute owner of 500 square yards.
3) Assuming for a minute that the said property was purchased by your father from his ancestral funds, ideally your father would have purchased his name given that he as a kartha of the Hindu undivided family comprising of himself, you and your younger brother.
4) The very fact that your father chose to purchase the property in the name of minor son(i.e you) and not in the name of younger brother (who was 3 or 4 years old at the time of registration of property) , goes on to reveal that the property acquired by your father in your name is your absolute property right from the time of its purchase.
5) Even your father or younger brother did not have any rights on the property standing in your name and their legal heirs(your late brother's wife and children) cannot have any rights thereof.
Hope this information is useful.