Have problems in selling property.

Hello Sir / Mam, My name is Ajay and I have a problem related to my father Mr. Ranbir Singh's property. My father has 4 brothers. Mahavir, Sukhbir, Rajender and Surjeet. 25 years ago my Grandfather partitioned his property among his sons. The property was on two places. One with less area and higher rates and the other with more area and too cheap rates. The low area one was equally distributed among Rajender and Surjeet and the 2nd one was equally between Mahaveer, Ranbir and Sukhbir. There was legal documents about that but Rajender has burned them and later died due to suicide. But my father have the written document and signed by all the brothers now. Now as we are shifting to other city we are selling our home to Sukhbir. He wants us to bring written and signed affidavit of Mahavir's, Surjeet's and Rajender's sons that there is no part of there in this land. Mahavir and Surjeet are agreed to do so but Rajender's sons are refusing to give affidavit and asking for equal part in the land we are residing since 25 years. I want to know what should we do.