Valaidation of document under muslim law

Sir, My maternal Grandfather had a home and few more acres of barren land in his name. he also had a mango garden in 2(two) acres. He had 5 daughters and 2 sons. in 1987, he got RS.25000/- from his 2nd son and made an agreement with him, stating that If he was unable to repay the amount within six months , then he 2nd son can claim the ownership of the mango garden. but in case my grandfather returned the amount within six months, then the agreement will be void. Later in 1990 my Grandfather passed away without leaving any will behind. now in 2016 his 2nd son is saying that he had not got the 25000 paid to my grandfather and hence he is the owner of the property, though the property is still in my grandfather's name. there is no other evidence to prove that the property had been transferred to the 2nd son. now my question is, 1.can the 2nd son claim my grandfather's property? 2. do all legal heirs (2 sons & 5 daughters) have any right over the property to share in 2:1 ratio as per islamic law. kindly advice us, Thank you.