Is it permissible to use a sum of money left by the mother and the aunt for the maintenance of the grandmother's house, without the participation of the other heirs in the costs, and would that be considered a sin affecting the deceased?

The heirs must be informed of the money remaining from the sale of the grandmother's land, as it became their property upon her death. They have the option to use it for house maintenance or to divide it among themselves. It is not permissible to dispose of the heirs' money without their permission, because ownership through inheritance is obligatory, and no one's money is lawful unless given with his willing consent. Such an act is considered a forbidden transgression. The heirs must be informed, and their forgiveness sought for your mother if she concealed the money from them.