The following does not imply that the pistol was left by will, but rather by informal request.
My who uncle who passed away earlier this year wanted me to have his S&W 686-2. He made this known to my family and my Aunt obliged
If that is the case and his aunt is not a CA resident, the firearm was transferred illegally between states.
Also, there is the issue of it being a non-roster pistol. Setting aside for a moment the possible federal offense that was committed, if his aunt is not a CA resident, state law has also likely been broken by bringing a non-roster pistol into the state via transfer of ownership.
If his aunt is not a CA resident, the prudent course of action would be to consult an attorney who specializes in firearms law, and post no further details on the internet.
If she is a CA resident, this
Do the transfer of ownership paperwork, pay the fees, do a DROS, wait 10 days while they keep the gun. Pick it up when all is approved.
is the proper legal procedure, all transfers in CA must go through an FFL(some exceptions, but none that would seem to apply here). The roster does not apply to handguns that were already legally owned in the state.