What is required of children regarding the fasting of their deceased father, who missed fasting several Ramadans due to illness, knowing that some of them are now unable to fast due to illness? Are they obligated to fast on his behalf or pay the fidyah, and how much is it?

If a sick person is unable to fast until they die, there is no make-up fast (qada') or expiation (kaffarah (definition)) due from them. However, if their excuse for not fasting ceased and they were able to fast but did not do so until they died, then one mudd of food (approximately 750 grams) should be given to a needy person for each day they missed. This is based on the Prophet's (peace be upon him) saying: "Whoever dies and owes fasts, then a needy person should be fed for each day." This is the view of the majority of scholars. It was also said that their guardian (wali) should fast on their behalf, but the majority of scholars interpreted this statement as referring to fasting for a vow. The feeding is related to the deceased's estate and must be given out by the heirs before the division of the inheritance. If the deceased has no estate, then the heir is not obligated to feed the poor, but it is recommended for them to do so.