B1/B2 - Dropbox Document Submission by Relative/Friend

Hi, My parents are eligible for dropbox appt for Visitors Visa renewal. Do they have to be present in person to submit documentation or can a relative/friend drop/submit the documents on their behalf? Any info is much appreciated. Thank you

May I know how you have determined the eligbility for dropbox appt for parent’s visitor visa renewal? I see other blogs saying there is no drop box for visitor visa.