Can you post a pic of one of them here or on Photobucket.com or one of the image sharing sites ?? (not face book) Take a pic of front and back and one of the bottom and we can look at each and get a pretty good idea if they are old cast iron or reproduction !! Did your grandfather say where he got them ??
The Nintendo games can be checked by looking at past and current sales on ebay !! That will tell you what each is currently selling for !!

https://www.pricecharting.com/console/nintendo-64

Here is a list of current prices on Amazon !!

How can I determine if they are replicas? Each piece is heavy. I received clearing my grandfathers house

First you need to determine if the cast iron is original or reproductions !! They have made repro`s for years !! Can you post a couple of pics of one or two ?? How did you get these ??
I do not think Avon ever made whiskey decanters !! They did make car decanters for mens aftershave !!