You give your close relatives a written power of attorney signed by you, and then put your handprint on it. At the same time, when submitting the case file, you also need to submit the original ID card of yourself and the original ID card of the agent. It is enough to show that the agent is entrusted by you. If necessary, you can contact the local sub-district office and ask it to prove the identity information of your entrusted agent or issue a certificate to the court.

I consulted the chapter on Civil Procedure Law and Participants in Litigation, and found that the written power of attorney requiring the parties to entrust an agent needs to be signed or notarized in front of the court staff.