It's complicated, but after you play a few times it makes sense. I agree it might be hard for somebody who's cognitively challenged.
Here's a good Youtube video:
https://www.youtube.com/watch?v=sv4FYUXe5VA . You could watch it and see if this is something you could see your parents doing.
Did you know that Wingspan's creator is local? I think she's (was?) a fed. There's a group of board game developers who get together at Board and Brew in College Park to workshop their games.