Legal Question in Civil Litigation in Pennsylvania

For what? And if the "parent" are pressing charges, this seems like a criminal issue, not civil. If criminal charges are brought, then you will need a criminal defense attorney.

I do not know who you informed them or how. If they are minors, you would have had to give notice to the child's parents.

For now, I would wait to see if you are charged criminally or sued civilly and then get a local lawyer as appropriate. The parents of the teen may just be bluffing. At most, I would send the parents a certified letter, outlining when the car was left at your property, what steps you took to have the owners remove it (provide a copy of any letter or recite the details of when, where and how notice was given) and give them the name of the towing place that got the vehicle.