Is it permissible to pay Zakat on money saved in hard currency if it is paid in local currency and from the father's money, knowing that my father and I consider our money to be shared and we cover the family's needs with the local currency?

Banknotes are a single class and are combined to complete the nisab. Therefore, there is no objection to paying Zakat for money in a certain currency from another currency, if the other currency is more beneficial to the poor, provided that the exchange rate of the currency is calculated at its rate on that day. It is permissible to pay Zakat from the father's money if he gives permission. If the money of each of you is distinct (hard currency and local currency), then each is obligated to pay Zakat on what he owns if it reaches the nisab and a year has passed over it. It is permissible to dispose of the other's money with permission. However, if the money is mixed, then each is obligated to pay Zakat on their share, as mixing does not affect anything other than livestock according to the majority of scholars.