Remaining area

Dear sir, In 1972 my grandfather has purchased 2:20 guntas of land from seller of total area against 3:26 guntas . in this land west side 0.29 guntas has been taken by water canal in 1950s. Seller was cultivating the remaining land at the time of purchase. After removing the canal limits that is 99 FTS from the centre there was only 2:20 guntas was there to seller in 1972. The same has been purchased and registered by my grandfather. As for that time the boundaries were mentioned correctly. They didn't mentioned remaining land 0.17 guntas in any boundaries. Now from past two years seller sons claiming that remaining land is there adjacent to canal only. Today also there is only 2:20 guntas was available after 99 FTS canal boundary. Seller is still alive 0.17 guntas in her name only, my grandfather is died on 1995. Now the land is in the name of my grandmother. I want to know.. 1)At the time of registration who has to say boundaries, seller or purchaser.( how do purchaser will be knows land boundaries) 2) who is responsible for not mentioning remaining land in boundaries. 3) is there any option to rectify the boundaries by appealing to court.