First lemmie give you some backstory to this for clarity.

I live in a two-home property formally owned by my deceased Grandmother, now left to my Mother. And I live with her and my brother in the back house while my Grandma lived in the front one. Anyways a few years ago her boyfriend that lived with us for a few years became hospitalized and eventually passed on, leaving us with all his stuff that his family has never come by to pick up or asked for his things, including his gun collection.

Fast forward to to now where we're clearing out all my Grandma's and her boyfriend's stuff, selling it or just throwing it out. We've either legally disposed or sold most of his guns away, all except one my Mom wanted me to keep due to everything going on. The gun in question is a sweet Marlin 1894 chambered in 44.mag/44.special, everything works fine and just seems to need a little TLC and its ready to rock.

Now this is the first time I ever had a gun and want to do everything by the book and nice and legal. So my questions are, how do I go about registering a gun that was left from my Grandma's deceased boyfriend who's family doesn't want it?