Does the estate still have them, or are they legally hers? Is she his mother (doesn't sound like it) or adoptive mother? I believe for either case there can be roster exemptions, which would be needed for any handguns not on the roster to be sent to his FFL in CA. Guns on the roster are no problem. Obviously can't be assault weapons, and the only common feature on ordinary handguns that is an AW is threaded barrels.
If the gun can legally be transferred to the man in question, there's no issue shipping them to the FFL. There can be issues with shipping a firearm to an FFL when it can't be transferred to the intended recipient, though, with respect to getting them back, IIRC. For a non-FFL to send them to a CA FFL is no issue. I forget if an FFL requires registration with CA DOJ to send them to a CA FFL or not. Other than possibly the latter requirement, the process is basically the same as sending them to FFLs in most other States.
Being physically disabled should not be an issue.