Long story short I think you just need to move out. I also don't really know what I can say about your parents... you're 22, taking away your car is punishment for a 16 year old. Don't put your dirty piss in there man, it's looking for any amount of THC over a certain threshold. Not worth it. Also, the synthetic alone will be enough. That's how almost everyone on the forums pass their drug tests. Please be respectful of your parents while you're under their roof though, they sacrifice a lot for you.
I'm honestly not sure what the answer is to that, but I feel like doing it is just unnecessary. I think you'll be fine with just the synthetic urine