The business of handling money and household affairs should be in your hands and surely this can be arranged. If you were to go to a lawyer and have papers drawn up to give you power of attorney, you could hire somebody to do the yard work and other things. And you could renew the insurance and so forth, and just let the car expense lapse, or sell the car. You might have to prove to somebody that your parents are unable to look after their own affairs. I feel that wouldn't be too difficult, considering the way they live.
Many old people fall into that sad and dangerous situation.
It doesn't happen suddenly, it happens gradually. You really do need help to be able to take charge. Social workers are paid to help people like you care for their parents in the best way possible. Don't think of it as interfering with them, all you are going to do is help them, in the same way that they helped you when you were young and needed help. Now it's your turn to take over.