What is the ruling on using the father's car and living in his house if they were bought with money mixed between lawful and usurious, and the percentage of usury is greater, and what is the solution in this case, and does that affect one's studies? And is the son sinful if he agrees to that and does not admonish his father?

If the father bought the car and the house with an interest-based loan, then they are his property, and he is permitted to benefit from them. He must repent and repay only the principal, unless there is a necessity.

However, if the father bought the car and the house with usurious money (bank interest), then these items are unlawful and must be disposed of by spending them on public welfare or on the poor, along with repentance.

The questioner is permitted to reside in the house if there is a necessity for study and no other shelter or ability to rent.

The prohibition stands if the majority of the price of the car and the house came from unlawful money (riba), because the consideration is given to the predominant element, and if lawful and unlawful combine, the unlawful prevails.

As for the case where most of the father's money is unlawful, but it is unknown whether the specific price of the car or the house came from unlawful money or not, then the money is mixed. Scholars have differed on this, and the fatwa (definition) issued by the network is that it is disliked (makrooh).

The questioner is obliged to advise his father and warn him against dealing with riba.