The ATF wants the 4473 Form on file, so they can ID, locate and confiscate.
Does MD allow private sales? If so, sell each one to him now for $1 (as formality, w/ no inheritance tax issues), and keep MS-Word receipts on file w/ your Will. Then he already owns them. No FFLs in his future.
Friday, “hopefully it will be ready”, when I pick up the Five-seveN I’m going to ask my FFL what the laws are. If that’s not clear I’ll have Mrs S ask whomever at her firm would know.