Here's what I've had some of my clients do:
Go to the gun portal and surrender the guns to the police. Print 3 copies of each EFA10.
Go to the gun portal and transfer the surrendered guns to transferee (nephew or grandson-in-law). Print 3 copies of each EFA10.
Grandfather-in-in law writes letter to police authorizing transfer of surrendered guns.
Grandson-on-law writes letter to police informing police that he will NOT return guns to grandfather-in-law unless he becomes properly licensed.
Uncle writes letter to police authorizing transfer of surrendered guns to nephew.
Nephew writes letter to police informing police that he will NOT return guns to uncle unless he becomes properly licensed.
Grandfather/uncle, nephew, and grandson-in-law all go to police station with guns, EFA10s, and letters to surrender guns.
Go inside with paperwork, and leave guns locked in trunk of car outside (properly stored)
Tell them you wish to surrender and transfer the guns.
If you're lucky, police will take paperwork and tell you to leave. Otherwise, bring in the guns, surrender them. and ask when they will be delivered to the new owners.
Notes: IAAL.
No limit on number of transfers when done as a result of surrender to police. No FFL required.