Once the division and registration of property is done, they are legally binding. However, if during his lifetime in 2015 your grandfather distributed the agricultural land between his children and legal heirs of deceased son by registering without any conditions or compel, it is unlikely to change. As - legally the property is divided or distributed and registered, he cannot withhold this division after nine years.
This division is likely nearly impossible to challenge in court, as litigation could only be lodged if serious grounds (fraud or coercion) exist following a very long time. So, his attempt at obtaining or changing the property division will likely be unfruitful. Always speak to a property lawyer for advice specific to your case, inorder that will help protect the interest. Take appropriate steps to file unused registration papers or whatever records were received in the correspondence back from 2015 with all other related documents regarding the land transfer.
In the event your grandfather does seek legal recourse, be prepared to object on grounds that it is stale and ancient or whatever else you come up with which supports finality of transfer. The defense should stress that the transfer was both voluntary and unconditional, thus making it final.