Is all the money that my father obtained from selling a house built with a usurious loan considered unlawful, and is it permissible for me to ask him to buy me a means of transport, knowing that he acts upon a fatwa that permits usurious loans for building in the countries of the Islamic Maghreb?

The impermissibility of an interest-bearing loan is related to the liability of its borrower, not to the specific item it was spent on. If the father engaged in the transaction believing it to be permissible, following the fatwa of someone who permitted it for him, then we hope he is excused. There is no blame upon him, nor upon the questioner, in benefiting from the price of the house.