Does my uncle have right in my fathers property

My Grand fa has two sons and three daughters. The younger son he has given for his brother(Who has no child) But no Adoptive agreement has done except in school ration card he has his adoptive father name). My grand fa has written all the property in my fathers name and in the same case younger son got all the property from his adopted father. Now my father younger brother is asking for equal share from my father. How can my father defendand protect property