Hello,
Thank you for posting your query.
In case the land which your grand father from his brother was self acquired property of your grand father's brother, then there was no need to take signatures from his son.
Whereas, if the property was 'ancestral', i.e., inherited from your great grand-father, then your grand father's son/daughter also has a right in the same.
Unless I get more details regarding the same, this is the only information that I am able to provide at the moment.
Regards,
Nishant
