Are the guns already in NJ? You didn't say what state your G-Pa lived in and where the guns are stored. I started a thread a week or so ago about how to give a C&R gun to my father who is a Fl resident and I'm a VA resident. The answer was that either my dad needs to get a C&R FFL (like I have) or go through the transfer process with an FFL in his state. I quickly discovered that I would find no real answers on this forum, not because the people here didn't know what they were talking about, but because you really need advice from a source like the BATF and the peoples republic of NJ (my Mom's from NJ). There could be some inheritance laws in NJ that cover this sort of thing.
At any rate, you could adopt me and I'll keep them in the family for you (the Virginia branch of the family)