I have a AZ NFA LLC that i am the only member of and i am not sure what would happen to the property if i passed away. In hind sight i wish i would have gone the trust route. In the future any NFA acquisitions will go into my actual family trust that we created to protect all of our assets not a phony one created just for purchasing NFA items.
I would say just make other members of your family members of the LLC, then any of those people could possess the NFA weapons also, but then they would also become owners of said weapons so only people you trust. Not an expert here but it shouldn't be too hard to add family to your LLC.