What is the method for making up missed Ramadan fasts on behalf of the deceased? And should the expiation (kaffarah) be paid for each day individually, or all at once? And is the expiation calculated for multiple years or just for one year, if the deceased delayed making up the fasts for several years?

If a person dies and was unable to make up for missed fasts due to a continuous excuse until death, neither making up the fasts nor feeding the poor is legislated on their behalf. However, if they were able to make up the fasts but did not, then it is permissible for someone to fast on their behalf, and a fidyah (expiatory feeding) should be given from their estate, or their guardian can voluntarily give it. The expiation does not multiply with multiple years of delay. It is recommended that the feeding coincides with the making up of the fasts.

Al-Nawawi stated in Al-Majmu': "Whoever dies owing missed Ramadan fasts, and had a valid excuse until death, then nothing is obligatory upon their heirs. However, if they were able to make up the fasts but did not before death, there are two opinions: The first is that it is obligatory to feed one mudd of food for each day from their estate, and it is not valid for their guardian to fast on their behalf. The second, which is the preferred view, is that it is permissible for their guardian to fast on their behalf, and it suffices over the feeding."