All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
You must withdraw the deposits and get rid of the interests by giving them to the poor and destitute or spending it in the general welfare of the Muslims.
If your brother-in-law (the husband of your sister) is poor and needy, then it is permissible to give the interest to him for him to pay his debt as he is eligible to receive this interest.
As for using the interest to pay your father's debt, this is not permissible; in fact, it is an obligation to pay his debt from his inheritance before dividing it. This interest cannot be used to pay his debt. The fact that the bank will obligate you to pay the interest is not a reason for you to save your money and pay from the interest because you are not allowed to make use of it; they are, rather, only lawful to the poor.
An-Nawawi said: "If one pays the ill-gotten money to the poor, then this money is not forbidden for the poor; rather, it is pure and lawful (for them), and one may also donate it in charity to himself and to his children if he is poor, because if his children are poor, they are eligible to receive charity; rather, they are the primary benefactors of charity, and he himself may take according to his need as he is also poor." [End of quote]