Legal vaidity of token sale receipt given for land sale

HI I’m a NRI and resident of US hence I need your help to know if I can deny to sale my property based on below situation. I’m seeking a suggestion based on the custom practice and human values to respect others. I’m aware that legally I can deny the sale, let me explain… Expectation from Forum: If as per custom practices if it is acceptable to deny the sale, let me know what my legal options …are. About Sale Transaction: We have small agriculture land (2000 Yards) which is located on highway, this land is ancestral property of my grandmother (she expired long back). My father’s brother who live close to property was approached by land purchaser and requested to sell the property. My father also gave consent over phone to sale the land hence my father’s brother took a token money of 1-2% of agreed purchased amount and gave signed receipt on a white paper. About Dispute: My self and two of my older brothers (one of them also in abroad) were informed about this, then we told our father not to sale this land, it can be used for a social cause (constructing a temple or something). This is a small bit and 25% of land will go for road expansion. As I highlighted question is based on human values, keep it aside the cause of denial is for social cause. As it is thought, within 24 hours, we informed the purchaser that we are not intending to sale the land and we told him to collect the refund amount. But the purchaser is denying to take the refund amount. He is insisting to sale the land. We tried our best to convince him with the local public. We offered him to pay if he had incurred any expenses towards brokerage to approach us. Still he denying and only demand he is having is to register the land. My father is 70 years hence he scared to face the consequences. He scared that , if this becomes failed transaction, the purchaser will influence locally to freeze the sale of our other agricultural land. This is small amount of sale I won’t make any profit out of this but insisting deny to sale the land for good cause. Also I don’t want to lose the land just by frightening with local guy. Question: Do I have right to deny to sale the Land after signing the receipt?. I’m thinking it is justified, as we have informed the party within 24 hours and also we are ready to refund the money along with expenses. If I have the right to deny to sell and if I’m not deviating any customs, I would like to fight for this, even if It costs higher. So, please let me know the options available for me?