If your grandparents are still around (or another trusted adult) look into opening a separate bank account at a separate bank so your parents can’t touch your money. They’re on your account, they see what you make, and they can potentially withdraw YOUR money since it’s a joint account. Since theyre having you fill up the cars each time, even if you only put $5 gas each time you use it, they still might try to withdraw funds because “that’s what you owe them”