Is it obligatory to pay Zakat al-Fitr accumulated over 25 years for 25 individuals, or is a smaller number permissible, and how is its amount calculated?

The father must pay Zakat al-Fitr for himself and for those he supports. If he was unaware of its obligation, he must pay it for the past years. You are permitted to pay your Zakat for the years you were under his care, provided you inform him.

It is permissible to give the Zakat for these years to one person or to several people. There is no condition to give it to a specific number, as long as the recipient's state of need does not change.

Zakat al-Fitr is paid in food. The weight of a "sa'" (ancient measurement) varies depending on the type of food; a sa' of flour is equivalent to two kilograms, and a sa' of rice is approximately three kilograms.