A Land (Pond) with multiple owner.

There is a Pond in our village ( Daag No 2753 , Khatian No- XYZ of Mouza Salanpur). It was inherited to 4 brothers after the death of the actual owner(their Maternal uncle). Brother- 1 presently dead and having his widow wife and 4 sons. Brother-2 is also dead and having his 2 sons. Brother-3 is also dead and having his 1 son & 1 daughter(Married ). Brother-4 is alive who have no son but 3 daughters (all are married). Brother-2 is my Grand father (my mother's father) . After the inheritance it was seen that Brother-1,3 & 4 have 20% each of the land and 2 son's of Brother-2 have 20% each. Now, I have bought the 20% part from the Son-1 of Brother-2 who is my Maternal Uncle. Therefore out of 100% i am the 20% owner of the Pond. I am willing to buy the whole part of the pond but at present they are not willing to sell their part. The case is Brother-4 want to sell his part but not willing to sell it to me. As he is not willing to sell it me he is intensionally saying a high selling price and also saying to buy the other property he is having at a time, which is not posible due to financial problem. this case what can I do legally to buy the whole part of d pond?