Nominee legal heir Dispute during redevelopment.

My cousin has lost his father when he was 6 year old. His mother and he was made to leave the house by her widowed sister in law from the house of his grandfather. His grandfather had 4 children viz. 2 sisters and 2 brothers. One sister stays in different district with her husband who has strained relations with the widowed sister and elder brother. After the death of grandfather in 2012 the flat nominee was his wife. She too passed away in 2019 and her daughter and his widowed aunt having her flat in same building along with elder uncle took the charge of society matters as nominees. My cousin and his mother had no source of income other than pension of his father and settlement amount received from the employer of his father. His mother served as a contact labor till covid while he has joined a private firm 6 months back earning 15k salary. The society is planning for redevelopment which needs agreement to be done with the owners. The society chairman is unwilling to provide any information to cousin as legal heirs and asking to give NOC to nominees to fulfill the process. This may cause loss of rights by my cousin and his mother. Cousin was given two option by his uncle and aunt 1. To give unconditional NOC or 2. Give money to them to release their claim under the condition that the flat cannot be sold or rented to third party. Please advise how this can be taken ahead?