What is the ruling on purchasing a car in installments with interest paid by the employee, and is it permissible to pay this interest from bank profits, and is it permissible for the family to use this car?

It is permissible to purchase a car by installment, even if the deferred price is higher than the spot price. However, if the bank pays the price of the car on behalf of the employee and then reclaims the price from him in installments with an increase, this is a usurious loan and is forbidden. Depositing money in a usurious bank is forbidden except out of necessity to preserve money in a current account. Whoever has engaged in usury must repent and dispose of the interest by spending it on the welfare of Muslims; he is not permitted to benefit from it. If a person buys a car through a usurious transaction, he owns it, while falling into a grave sin. As for your riding in his car, the general principle is that it is permissible, but it is preferable to refrain from it as a deterrent to him and a denouncement of his action.