Is it permissible for my father to work in a trade financed by a usurious bank? And what can I do to convince him to abandon that? And would all his possessions be considered unlawful in this case? And what is the solution?

Your father is not permitted to borrow with usury, whether for trade or otherwise. His justification that what he borrows is spent on permissible things is invalid, because a Muslim is required to acquire money from a lawful source and spend it in a permissible way. So, whoever acquires money from an unlawful source and then spends it on permissible things is sinful for his initial action. He must free himself from usurious contracts. As for the profit he earned from his trade using those usurious loans, we have favored the permissibility of taking it.