Is it permissible to pay part of the Zakat for the repair of a father's car and the other part to cover the expenses of siblings, knowing that the father is in debt and unable to meet these expenses?

Zakat is obligatory without delay, and it is not permissible to postpone it except for a valid excuse. The general rule is that it is not permissible to pay zakat to one's father because the son is obligated to financially support him. However, it is permissible to pay it to him if the son is unable to support him, or if it is for paying off the father's debt, because the son is not obligated to pay off his father's debt.