FIDs are useless, he can't possess any handguns with them and most rifles either.
He needs to get his LTC before he can take possession.
If the guns are willed to him, the executor of the estate can personally give him the guns (assuming he's licensed to possess them) with NO FFLs involved. He just does FA-10 Registration (description of gun, and his info, NO info on source of the guns) within 7 days of receiving the guns in MA.
If he were to involve an FFL, any handguns that aren't on EOPS List would be "dead in the water" and can't be transfered to him (unless they fit the grandfather clause of being in MA on/before 10/21/1998). Fed and State law allow direct inheritance with no FFL involvement.