Can a son-in-law or other male relative perform Pind Daan?

Yes. Traditional Hindu scriptures acknowledge a clear hierarchy when the son is unavailable: the grandson, great-grandson, wife, daughter, daughter’s son (Dauhitra — especially praised in Garuda Purana), brother, nephew, and other sapinda relatives are all eligible. A son-in-law (Jamata) can also perform Pind Daan when closer relatives are unavailable, and a qualified priest (Ritwik) may perform it on behalf of any family. The key requirement is the correct gotra invocation and sankalpa — the relationship of the performer to the deceased is secondary to the ritual integrity.