Here's a listing for a Wii bundle from GameStop, probably more expensive than you'll find on Craigslist, but more reliable and you can return it if it has problems. It has all the cables, etc. you need to hook it up to a TV, you may need to get batteries for the controller, though - and you may want to get an extra one if he wants to play with someone else at the same time.
https://www.gamestop.com/wii/console...rbished/165838
You dad won't care about the Mario games, but the grandkid(s) will like them.
But it also has Wii Sports, which is a collection of games like tennis, golf, boxing, etc. It's probably what you saw in the hospital. My wife is a memory care/assisted living nurse and they play this in activities for the residents. There is a sequel, Wii Sports Resort that he might like as well
https://www.gamestop.com/wii/games/w...ame-only/76050
The controller can be pointed at the screen and "fired" like a gun - most of those games may be too violent for your dad, but there are some hunting games like this
https://www.gamestop.com/wii/games/c...ter-2012/91878
If your Dad has issues standing, don't bother with Wii Fit and the balance board - you have to stand on it to make it work.
The WiiU was basically the next "upgraded" version of the Wii, with it's big gimmick playing everything on a controller that had a screen on it - I wouldn't bother with it - probably way more than your dad needs and he might find it too confusing.