The "responsible party" is the party who is found to be liable for the occurrence that forms the basis of the suit. Hence, there is no "responsible party" until the case has been adjudicated.
Yes, The at fault party is responsible.
No
they cannot be sued because they are not responsible for it after they sold it
Yes, of course you can be sued for anything...The fact that neither vehicle wasn't insured does not obsolve the 'at fault' party from being responsible for the damage they caused to the 'innocent'.. (subject to state laws of course regarding recovery by an uninsured)
defendant
They can be sued for a breach of the agreement. Co-signers are equally responsible for any default regarding a lease.
Of course, and they can be sued if they don't pay.
The debtor is the party responsible for payment obligation on an account.
They could be sued for a breach of fiduciary duty. They are responsible to the court to execute the will or the state's intestacy laws.
Unofficial colonial groups were most responsible for the Boston Tea Party.
The owners of the vehicle can be sued. The driver can be named, but as a minor, the parents are going to be held responsible.
A seventeen year old can not normally be sued in court. They are not yet an adult. Their parents can be sued, as they are responsible for the 17 year old.