The NYPD will probably tell them they have to transfer it out of the city via an FFL...because they aren't technically allowed to take the guns our of their apartment unless it's for target shooting in nyc or hunting...
I thought that was part of the case the Supreme Court looked at a few years back, where in NYC you could not even take your guns to another house you owned in state, or to another state for practice, matches, etc, the stated idea being that people were going to drive around with their guns, claiming they were going someplace out of the city, and then if they got cut off making a turn, a once law abiding citizen suddenly runs back to their trunk, unlocks the trunk and locked case, loads the gun, and commits murder.
After the SC took the case up, New York did the Cheat and Retreat move, where they suddenly changed that law to allow for transport of your guns away from your home, to avoid the SC reaching a ruling in the case and striking down other crap laws.
So I think you are allowed now, even in NYC, to travel out of the city with firearms and not just for hunting or to the few ranges in the City.