I'm not really sure that they want to understand it. If they are fine wth their reality, why would you try to make them understand? it took my grandma a couple of month to learn how to use a smartphone for messengers and online video calls. I cannot imagine the situation where she would need to use crypto.
It's just a choice.
You can teach them if you want to and let them understand. As long as they have their mental consciousness and understanding, they can understand bitcoin even it will take days, weeks or a month or two.
You ask your grandma or grandpa if they are interested to an "internet money".