How should one deal with eating and drinking from the father's money, the source of which is banks, while avoiding cutting off family ties and destroying family life, and is it obligatory to demand that he stop dealing with banks?

A distinction must be made between money that is inherently unlawful (like stolen money) and money that is unlawful due to its acquisition (like money obtained through deception or usury). The former is forbidden to everyone, while the latter is forbidden only to the acquirer. It is permissible for someone other than the acquirer to deal with it if they obtain it through a permissible means, as evidenced by the Prophet's (peace be upon him) dealings with the Jews and his eating of their food, even though they engaged in usury.

If the acquisition of unlawful money is based on following the fatwa of a scholar who deems it permissible, then its owner is not sinful. It is permissible for one who believes in the unlawfulness of this acquisition to partake of it, and to advise the acquirer to repent.