Assume your grandparent needs a new basic laptop and is asking you for advice on what to get. Assume he or she uses it for bill paying, surfing a little social media and watching videos. What would you recommend?
Given your description, my first stop would probably be a local retailer of some type (Costco, Best Buy, Walmart, wherever) where they could actually get their hands on a sample laptop...for a few minutes.
Primarily to evaluate keyboard feel and screen quality. That's liable to be more important to a basic user than finer points like CPU, drive capacity, RAM amount.
You'd like to know something about reliability/longevity, but that is mostly just hoping with crossed fingers.
No need for Windows Pro, no need for more than 16 GB RAM (or even 8); no need for large capacity drives, no need for even semi-sophisticated graphics; no need for more than a mid level Intel i3 equivalent.............BUT.............you may have to accept some of that stuff simply because you can't custom-configure a laptop.
Might pay some attention to return privileges from the vendor. I think Costco is pretty good on that score.
Bang-for-the buck, you are probably better off with a desktop, but a strong requirement for portability may eliminate that possibility.
Maybe a second-hand laptop with a 17.3" screen would be a good choice for them. Even though they requested a laptop, they seem to have already decided on a permanent location, so they probably won't be moving the computer around much.