Property

Sir/Madam, My dad sold our property in 1997 which was willed by my grandmother to only grand sons ( Me & my brother), that time we were in school ( Minor) and we signed the document without the knowledge that the property belongs only to my brother and me, as per the buyers request my father, my sister have also signed for the sale of the property. but later when I came to know that their signatures were not required. As my sister was 10 yrs elder to us and was married at that time took advantage as we did not know any thing about deal she had managed to get around more than 75% of the sale money from my father. kindly advise if we can now file a case to get our share or at least some thing form the sale. Kindly advise. Thanks & regards Jack