The property was divided as per the court decree but the elder son sold off the property before the decree.how did je do so?that was illegal. Anyway...you didn't object to it. Then his son is demanding share in the property which is your share...He cannot do so. He has no right to any share. You have a share in your father's share as it is an ancestral property.
Caveat is an application filed in the high court wherein in case a case is filed against you you know beforehand.