My Mom was born and raised in Newark in the 40's and 50's. The area was called Vailsburg, near East Orange I think. I think my great grandfather was the postmaster of Elizabeth new Jersey back in the 30's/40's.
If you end up reporting the firearms and they have to be disabled, plead for them to let you keep them in their non-working form as heirlooms, or see if they can be donated to a war museum (in their working form preferably) in honor of your ancestors. Myself, I would try anything legal rather than have the government (ATF or local) mangle them in any way. Just a thought. I feel for ya bro!