I think a transfer between residents of different States has to go through an FFL under the 1968 Gun Control Act. As I understand the California law, an individual may ship to a Ca. FFL without registering with the Cal. DOJ. Out of State FFLs have to register.

Relationship is irrelevant. Father could certainly travel to Ca. and visit his son's local FFL and complete the transfer that way. Otherwise son is going to be holding an illegally transferred gun...Geo