Nery (or Neri) looks very unusual for a
German name. Are you really sure that your grandmother's husband was
German?
There are no
German names that have a natural short form or nickname like Neri or Nery.
There is a Norwegian name Neri and Neri was also used in Italy. The Biblical character named Neri is very marginal (only occurring in a genealogy, no story about him) and Biblical naming wasn't as popular in Germany as it was and is in the USA.