Sounds like a very nice collection. I would reach out to one of the many auction houses and ask for some support and guidance. Love of the Game is one that comes to mind.
http://loveofthegameauctions.com/
Also depending when you put these in sleeves if it was done in the 70’s or early 80’s. You may want to check them. Many of the early plastic protectors had a chemical which actually damaged cards so be careful and check.
In terms of grading should you decide to get them graded. Both SGC and PSA are good choices. I like SGC but it's a personal preference.
Another option is to do a bunch research via eBay and others and use our own BST here to sell cards that you have figured out a rough value on by doing some research.
Wish you the best and keep a few if you can as they were your grandfathers.
Cheers,
John