They currently have 7" Samsung tablets from about 6-7 years ago. No more updates to the version of Android, and some apps are no longer able to update because of that. So ideally something as recent as possible that's likely to keep getting updates for another few years.
Budget is as little as possible obviously, but I only want to suggest a quality tablet for them - 2GB RAM minimum, ideally more (they don't have a lot of time left, I don't want them wasting it waiting for slow tech). They don't play any games, mostly just emails, reading Kindle books, Skype, looking at pictures and accessing some reference material via apps (such as lesson manuals, etc).
7-8" are both fine sizes, although 8" is better due to poor eyesight at their age. 10" is too large/heavy though. Samsung seems to have a few options, but I can't tell which models are better/newer because rather than using sequential numbers, they've named their models A and 8 and Note sigh - so any help is appreciated.
https://m.ebay.com.au/sch/i.html?_nkw=Fire+tablet+8&isNewKw=…
Amazon fire tablet is good for the price vs specs vs features. Just need to side load Play store after boot. I gave a bunch of 7" tablet to my cousin kids a year ago. Still solid and works with almost all android tablet applications.