What is the ruling on disposing of Zakat funds that are undecided as to whether they should be disbursed by the bank, given to a patient with kidney failure, or to a widow with young children, or to a divorced sister with two children, or to search for another deserving recipient, or to keep them?

It is not permissible to withhold zakat on wealth; it must be disbursed immediately to those entitled to it, in order to avoid the severe warning for those who withhold zakat. Allah has clarified the categories of zakat beneficiaries in His statement: "Indeed, zakat expenditures are only for the poor and for the needy and for those employed to collect [zakat] and for bringing hearts together [for Islam] and for freeing captives [or slaves] and for those in debt and for the cause of Allah and for the [stranded] traveler." Your sister has a greater right to the zakat if she is poor and her income is not sufficient for her basic needs. If she is not in such a state, then seek out those in greater need. It is permissible to give it to a sick person who cannot afford the expenses of their treatment. If you do not know any eligible recipients, then appoint a trustworthy person to disburse it, and do not leave it with the bank.