Daughters file the partition suit

Grandfather have arround 15 acres land. In 1992 he made a partition with his 5 sons, and 5th son got 2.5 acre and another survey no 6 gunta has his share. Similarly 5th son sold the property 2.5 acre with his wife and his 1st daughter age 16 and second one age is 3 years minor's made them parties in sale deed and sign by his father has legal gaurdian and sold the property to someone. Later now the daughters file the partition suit on sold property and sale deed null and void.I am purchaser son.