Legal opinion required for ancestral property.

My grandfather's self-acquired property- is due for sale now and my grandfather passed away. My grandfather has one son and two daughters. My father and two of my aunties entered a family agreement stating that the “grandfather's self-acquired house property should be handed over to the grandson as a token of love (me) and my aunties received my grandfather’s money in construction of their houses, signed by all the three members (my father + two aunties and as a witness signatures by my aunties husbands) and Notarized the agreement in the year 2000 (my father and aunties also passed away)

Now I decided to sell the property, buyer is demanding NOC from my sister and my auntie’s children. Please help me, is it required NOC from my sister and aunties children’s or is there any other legal provision to avoid , because as of now they are not claiming anything, my worry is if I request signature particularly, they may demand money. What are my rights on this property? How to get over this issue.