A Google search reveals some sites with information about records for Nizhnyi Novgorod.

FamilySearch has images of revision lists up to 1858, so they may have records of your great-grandparents, but these are unindexed records (images only). 
https://www.familysearch.org/search/collection/2115663

Here is an article about the 1897 census in Nizhny Novgorod: https://vk.com/wall-56122476_3395?lang=en 

Here is an article about the central archive for that region:
https://dissertationreviews.org/jll-charge-needs-image-ok-central-archive-nizhnii-novgorod-region/ 

Here is a listing of archive fonds that may have 1897 census records for that region (in Russian, but use Google Chrome to translate it): 
https://arch1897.histcensus.asu.ru/regions/#713

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