I’d just sell the entire lot to a FFL dealer. If you want to know what they are worth (private sales, not to the dealer) look for the same models on Gunbroker, Guns International, or Armslist. Figure that the dealer will probably give you 50% of that.
The Winchester 840 is an inexpensive gun, and if the rest of the bunch are inline in terms of relative quality, you’re not sitting on a gold mine. There is always the possibility of a “ringer”.
The grandparents were poor common folk, we don’t expect to find anything of substantial value, but as you say, there’s always the possibility of a “ringer.”