My grandfather purchased a property in 1933 vied registry now my grandfather died in 1979 leaving 4

My grandfather purchased a property in 1933 vied registry now my grandfather died in 1979 leaving 4 sons & two daughters & wife In 1988 my grandmother died and in the same year we have an oral settlement and memorandum among the 4 brothers that the said property will go to one of the son ( My father) who will give the three brothers money against that , and will also leave his share from some of property of my grandfather as per the valuer, there was a registered relinquish deed among the brothers in 1997. Few days back my cousin brother who's father has relinquished his share in favor of my father has sent a legal notice that this property belongs to the grandfather so he is one of the Coppertone and he also have right.