You ask the community to issue a letter of recommendation to become your nephew's entrusted agent, and the nephew issues a power of attorney, indicating the authorization authority.
Because China's Civil Procedure Law stipulates:
The parties and legal representatives may entrust one or two persons as agents ad litem.
The following persons may be entrusted as agents ad litem:
(1) Lawyers and grassroots legal service workers;
(2) Close relatives or staff members of the parties concerned;
(three) citizens recommended by the community, units and relevant social groups where the parties are located.