What should the questioner do with her deceased mother-in-law’s share of the inheritance, which has not yet been divided, knowing that the will stipulated spending on the mother as long as she remained alive, and that the joint sum between the spouses is part of the inheritance?

The mother of the husband has a share in the inheritance of her deceased son if she dies after him. Her share is one-sixth due to the presence of a lineal descendant. Her right to inheritance is not forfeited by her being ill or losing her mind, because it is not a condition for inheritance that the heir be sane or healthy. If the mother dies, her share is transferred to her heirs after her. As for the husband's will to spend on his mother after his death, it is not binding, whether he willed that the expenditure be from the estate or from private funds. This is because the estate belongs to the heirs, and spending on her from your private money is not obligatory for you. Rather, the original principle is that it should be from her own money or the money of her children. If you spent on her with the intention of charity, then you cannot retract the expenditure. However, if you were compelled to spend on her from your money with the intention of recovering it, then you can recover what you spent. The presence of money in a joint account does not prevent inheritance, and the amount waived by the heirs is considered valid if the waiving party is an adult, of sound mind, and acts willingly and voluntarily.