Yes, your nephew would need the RCIA process. Typically it lasts for 6-12 months and culminates with the individual receiving all 3 sacraments of initiation (baptism, 1st communion, & confirmation) at the Easter Vigil.
Your situation would depend upon what your local parish does. Many parishes lump together unbaptized persons with Catholic adults who only need confirmation and confirm them at the Easter Vigil. Some parishes have a separate adult religious education program for such adults and have them receive confirmation at a Mass other than the Easter Vigil. So you would need to contact your local parish to inquire what their process is for Catholic adults who only need the sacrament of confirmation.