Is buying a house in installments from a non-Islamic bank, in order to save siblings from eviction, considered haram and usury?

Purchasing goods through a bank takes two forms: The first is prohibited, which is when the bank acts merely as a financier, lending the customer the price of the commodity with an increase; this is usury (riba). The second is permissible, which is when the bank genuinely purchases the commodity and then sells it to the customer for a higher deferred price. This is called Murabaha sale for one who requests a purchase. It is not permissible for the bank to sell before it has purchased the commodity. The brothers' need for housing does not permit usury, because the harm can be averted by renting.