[Aguila Blanca]

Based on what you wrote, I believe the transfers were illegal.

Federal law provides that firearms inherited either by bequest (stipulated in a will) or by intestate succession (the person had no will and you inherit under the laws of the jurisdiction) can be made directly -- even interstate -- without going through an FFL. It's not a "familial" exception -- it's based on who inherits.

In this case, I assume the wife/widow was the person who actually inherited the firearms. That means when she gave them to the brother-in-law, they were interstate transfers. Interstate transfers of handguns have to go through an FFL in the recipient's state of residence. Interstate transfers of long guns (rifles and shotguns) can go through an FFL in either the transferor's state of residence or the transferee's state of residence.

So the right way for them to have done this would have been to find a local FFL, both of them drive over there with the guns, and pay the local FFL to process the transfers.