What is the Islamic legal ruling on dealing with a stepmother who accepted a sum of money in exchange for waiving her share, and the position of the sister who demands an apartment for her son, and is it permissible to sell the property while compensating the males for what they spent on their apartments?

It is permissible for the brothers to pay a sum to the wife in exchange for her relinquishing her share of the inheritance, if she agrees, and this is called mukharaja (mutual release/settlement). As for the sister's request for the apartment, there is no obligation to grant it unless all adult heirs agree. She has the right to her legitimate share. If the heirs agree to sell the property, the brothers may claim the value of the finishing works they carried out if this was done with the permission of the other heirs.