Property dispute

My father purchased a plot and constructed a house and died without will. my mother was living there with her divorced daughter. we were 3 sisters and 2 brothers. due to disputes between our divorced sister and mother all of us signed an unregistered agreement on plain paper in presence of 2 witnesses. as per this agreement 50% house including all rights was given to the divorced sister and after her death it was mentioned that this 50% house including all rights will go to only daughter of divorced sister. map was also drawn. other 50% was dedicated to mother and after death of mother it was to go to remaining 4 children 2 brothers and 2 sisters. All 5 children and mother had signed in presence of witnesses. Now our mother expired, divorced sister expired and one brother( who had no living wife) having 3 children also expired.... Questions....whether this agreement is valid if valid then 50% goes to daughter of divorced sister and out of remaining 50% 12.5% each to 3 living children and remaining 12.5% to be divided equally to 3 children of our deceased brother. Q2. If it is not valid then property will be distributed 20% to 3 living children and 20% to daughter of deceased sister and 20% equally to 3 children of deceased brother