Is it permissible to buy the share of one of the heirs in an apartment partially owned by the deceased for less than its value, due to inability to pay more, knowing that the apartment is in the father's name and the amount paid was equally divided between him and the mother?

It is permissible to pay a sum of money to the brother in exchange for his relinquishing his right to his father's share of the apartment, for the right belongs to him and must be paid to him. He is allowed to relinquish his right, or part of it, if he is an adult and of sound mind. As long as he agrees to a compensation, it is permissible to pay it, even if it is less than the value of his share.