Used cars from private sellers are generally always "as is" - let the buyer beware. (unless there is some type of agreement to the contrary) He should have had the vehicle checked out before he bought it.
No, not illegal at all. The only time there "might be" a problem is when foster children are involved or when a child is being considered for adoption.
Used cars from private owners are generally sold ":as is" -let the buyer beware unless you have an agreement to the contrary. You should always take the vehicle to your own mechanic to be checked out before buying.
It sounds like you need legal help. You can contact your local legal aid society or check with your county or state bar assoc. - sometimes they can suggest a lawyer who will take your case pro bono (without cost to you).
When you go to court, plead not guilty. If you cannot afford a lawyer, ask that a public defender be appointed (a PD is a lawyer). You need to discuss your options with a lawyer.