What is the ruling on purchasing a property built with a usurious loan, with part of its price paid to the seller and the other part to the bank in usurious installments? Does this count as engaging in usury, even though the buyer did not take a loan from the bank?

Usury is one of the greatest prohibitions, but the sin in borrowing with it is related to the borrower's liability, not to the money itself. There is no harm in buying something that was purchased with a usurious loan, although it is better to avoid dealing with someone who possesses unlawful wealth. If you wish to pay the full price immediately, there is no problem. If you wish to pay it in installments, then the seller should handle the transfer to the bank.