First, you don't need to use the house as collateral to buy a car now, but use the car you bought as collateral. If you can't pay back the money, they will take back your car.

There is no conflict between buying a house with a second loan and buying a car. As long as your mortgage repayment is overdue for no more than 5 times, there is basically no problem. When buying a car, the guarantee company only needs you to prove that the house is yours according to the house purchase contract and invoice, and the third company can give you a proof of income.