this is much more easier for old folks, just point and click (airmouse is cheap too) if they are able to use their Android phones, no problem adapting to Android box basically everything is the same.
For just $150 bucks, no need to invest in another monitor or spend on a PC unit powerful enough to run Windows. You can't teach seniors Windows but you can teach them Android (I've done it)
Take note the type of Android box you buy though, some China made ones will come with their own Interface and can can quite confusing. You should be getting those with vanilla Android Google interface (comes with Google Playstore) which can see all apps at a glance. I recommend the MiniX NEO (my mum uses one) and you can drop by their SLS shopfront for a demo to try out before ordering on Lazada/Shopee.