Sincere thanks for the update. We rarely hear what happened with these threads.
Lend them the car for the year and don’t worry about it. A car seems like a big thing and a year seesm like a long time when you’re young, but as the years pass you’lll realize that neither is really what it seemed. A year will seem short, a car will seem far less important. But your parents will grow with importance until that inevitable day comes when you no longer have them. Then the memories of what they sacrificed for you, and the memories of having made a small sacrifice for them, will be the most important things you have.
You’ll often hear people say “I wish I’d done more for my mom (or dad) when she/he was alive”. You’ll NEVER hear anyone say “I wish I’d done less for my mom/dad when she/he was alive”.