Does buying two computers in installments from a brother who owns the money, and he pays their price in cash to the seller, then adds 25% to the original price in exchange for the installments, constitute a trick to circumvent usury?

There is no objection to the aforementioned transaction, which is a form of murabaha (cost-plus sale) involving installments, and it is permissible in Islamic law. It is commendable if the intention behind it is to show leniency towards the buyer, and it is permissible if the intention is profit and exchange. It must be known that it is not permissible for the seller to take an increase on the debt if the buyer delays in paying the installments, because that is prohibited riba (usury). However, the seller may mortgage the sold item until he collects his debt.