So, basically, you would be getting two Pokemon with Nincada's IVs, EVs, and Nature? Or would Shedinja not have Nincada's EVs, IVs, moveset, or Nature since it's technically a different Pokemon?
"Shedinja inherits the same personality value, IVs, EVs, OT and ID number as the Nincada that shed it. Among other things, due to retaining personality value, if the Nincada was Shiny, Shedinja will be Shiny as well."
Hope I helped :)