Please give legal advice on notarized agreement of sale done in 2006

A property dispute over a grandfathers property which was willed to grandsons is going on for the last 20 years till now in the court of civil judge senior division..during he pendency of the suit if one of the grandsons gives a notarized agreement to sale to a third person with a condition that he will settle the disputes if any in the court of law and shall get the registry done in the third party name ..the agreement of sale was notarized in 2006 with the amount of 31 lacs paid to one of the grandsons for his 1/3 share . My questions are as under: 1. During the pendency of the suit is the notarized agreement to sale valid ? 2. can the third party file case under specific performance act to get the property registered in his name through court when the case is still pending in the other court ? 3. what else can the third party use that notarized document for ? Please advice