In some states a US military knuckle knife, especially a Mark One is "illegal".
These laws are more directed toward sketchy people actually carrying one on the street.

However, as antique's of great value, and that you aren't going to be carrying it around, you should not have any problem.
Yes, if you get into trouble for something else it could be used to add on charges, but no one is going to be much interested in a knife over 100 years old and of high collector value.
The most probable risk would be in New York City.

Again, the trick is to not be carrying it and not being a criminal type.
If you put them in a display case I'd think any risk would be minimal.

 

I've also read of some localities charging ex-cons with carrying a dangerous weapon when they were caught with pen flare guns. Not sure of the outcome. And, of course, anyone can put about anything in print or on the internet any more, but....

 

I had WWI LF&C knife in the collection for years when I lived in NY. No problem since I didn't wave it around at anyone. LEOs in our gun collector circles didn't care about it either.

 

while the above posts are correct, it is still against the law, as written, to own some in NY,

the decision is yours to make,

FWIW, I picked up an estate a couple years ago in NY, a full 1/3rd tp 1/2 of what I bought was not NY legal any longer, including a handful of real and repro trench knives (knuckles)

the family wanted it all gone just in case a health care worker for a family member ratted them out,,

they wanted to avoid the Film at 11 pics of a pile of stuff not NY legal any longer spread out on the front lawn,

 

while the above posts are correct, it is still against the law, as written, to own some in NY,

the decision is yours to make,

FWIW, I picked up an estate a couple years ago in NY, a full 1/3rd tp 1/2 of what I bought was not NY legal any longer, including a handful of real and repro trench knives (knuckles)

the family wanted it all gone just in case a health care worker for a family member ratted them out,,

they wanted to avoid the Film at 11 pics of a pile of stuff not NY legal any longer spread out on the front lawn,

Their loss was your gain! Sweet deals were had, no doubt!

 

My advice is find out what the laws are where you live and abide by them.

You can't use the excuse (in court) that you purchased an item that is illegal to own where you live because it is legal to own somewhere else.