According to Precious-metal-refining.info, Nickel silver is named for its silvery appearance, but ironically it actually contains no elemental silver.
Nickel Silver via kwout
Nickel silver is different from plated silver in that nickel silver is not plated with silver and does not contain any real silver at all.
Plated silver is metal that is actually covered in a very thin layer of silver. EP and EPNS are other markings that indicate plated silver.
Given that nickel silver has no actual silver content, it is not worth anything to precious metal refiners. Unfortunately, there is nothing of value to extract. With that being said, your pieces still might be worth something if you try to sell them on eBay or to a scrap metal dealer.
Tip! Get information on the characteristics and common uses of nickel silver and identifies typical problems associated with this material along with common causes of its deterioration at GSA.gov.