I've seen this discussed, but really, how could they not know he was in jail? He lived with them. If he didn't show up for several days, but his car was still there, they would be really concerned that he might have either harmed himself or someone had harmed him. They knew he was being investigated in Christina's disappearance. They would most likely have contacted LE, to say he was missing, and be told that he was in jail.
But more than likely he contacted them from jail, and told them what the charge was (stolen phone, not connected with Christina) JMO.
Perhaps. I'm not claiming to know for sure, either way. But it's been my understanding - just based off of what I think I've heard here before from others - that it's said they didn't know he was in jail, until he was already out.
I'd say this. Is it POSSIBLE that he was in jail without his parents knowing? Sure. We can come up with speculative explanations, I'm sure. What happened, happened, and if they didn't know, then they didn't..
As for the car, it could have been towed and impounded, while he was in jail. More likely imo, he was arrested at work, and his car sat in the lot there.