I think the idea of having all the icons in one place is a good idea but I am not sure how an elderly person would get on with a touch screen over a keyboard. Not so much of an issue with iplayer but typing in web addresses, emails etc may be more taxing.
couple of options. One would be to get a Bluetooth keyboard also but you are adding to the complexity. Alternatively a cheap Windows 8 laptop with all the important icons on the start screen. Nice big icons to click the mouse on.
Take them to PC World and have them play with a tablet and see how they get on with it and decide from there.
Final option and whilst I wouldn’t go near one even if it meant never using a computer again would be a Chromebook. Loathe though I am to recommend it that would be my personal prejudice getting in the way of suggesting something that actually might be just the tick here.
Cheers
Danny B