How can one make up for the fasting days of a father who did not fast throughout his working life, and a mother who did not fast in her early years of puberty due to ignorance, with neither of them remembering the number of missed days?

If someone dies and owes fasts that they missed due to a legitimate excuse such as travel or an illness from which recovery is expected, it is recommended for their guardians to fast on their behalf. If they die before being able to make up the fasts, there is no obligation upon them. However, if someone abandoned fasting out of negligence, neither is making up the fast obligatory upon them nor is it valid if they do so. If you do not know the number of days the deceased missed, then fast what you believe would absolve their responsibility. It is permissible for the heirs to share in making up the fasts, and if it becomes difficult for them, they can feed the poor on the deceased's behalf. As for women, any fasts they missed due to a legitimate excuse such as menstruation, travel, or illness must be made up. However, if they abandoned fasting out of negligence, making it up is not obligatory upon them.