Also look on the back, any labels there?
Does granddad remember where he got them? How large? How long has he had them?
I don’t think you’ll be quitting your job over these, but they may have some resell value on ebay over 99 cents!. There are collectors of the Wanamaker gallery, for instance, but “value” for these is pretty low in the grand scheme of things. There is value in old paint by numbers, but sentimental value in them and these almost certainly trump the amount of money you can get for them, if you like them.