for old folks, your first criteria is 'easy to navigate'.

if you are refering to astro on the go apps on android tv, actually it is not suitable for old folks because u need a mouse to navigate. if you are refering to iptv apps that has astro channels then that is another question altogether in terms of legality, reliability etc.
if they only want to watch free-to-air malaysian tv then you can consider mytv. no need internet also 

*Brand
*Firmware stability and future updates..ideally simple click for OTA updates.
*Minimum 2GB RAM (ideally DDR4), 16GB storage for pure streaming, no gaming etc... if plan for more.. ideally minimum 32GB.. Else 64GB storage for heavier usage.
*Ethernet port.. Ideally Gigabit.. 100M "might" still be okay.. but definitely go wired if you can.
*User Interface... Has to be easy to use and remote directional buttons-friendly.

Hard even for me to say that getting elderly folks an Android box + ehem IPTV services is an actual upgrade.  ... But hey, if they are willing to learn and okay with it? You can save a lot and get way more content too.

Hi...I think for starters i'm unsure if this is the right place to discuss such..As it's off topic.. Nevertheless, here are some info to kick you off.. If you find an appropriate thread to continue this, just tag me and I'll drop in.

I believe you need to decide if you need a proper Monitor (to be used almost exclusively with a PC via DP connection) or a Smart TV (to be used jointly with an external player and PC via HDMI connection). Reason is, as much as some use TVs as monitors (cuz larger size and cheaper), IMO they are different and should be viewed differently. Besides sitting at arms length from a TV everyday WILL ruin your eyes over time. Got a few friends kena.

Monitors: I'd say focus on the text clarity & color reproduction.. Then only if got speakers or not, refresh rates la, etc.. And if you game, flickering, Nvidia G-Sync and or AMD FreeSync la etc... I'm not a hard-core PC gamer and thus currently using the Philips 27" 3840 x 2160 IPS 4K UHD Monitor (276E8VJSB). It's an excellent "no frills" entry-level 4k monitor with superb colors & text clarity. No issues running full 4K res all the time. Contrary to some beliefs, the icons and text size is okay. Don't have to windows-scale like crazy. Has its downsides too, but i find it negligible. Major downside for me would be that I didn't get a larger screen.. I'm used to it's size but 32" i think would be more ideal for my recent usage. If you have to spring for 4K res? Ensure that your PC can actually handle driving such a monitor, be it for normal usage or gaming (especially). Monitors like this can also be used with Android boxes as it has 2x HDMI ports and a DP port for the PC.. Switching between ports is automatic and can be manually switched too. Just an option.

TVs: Samsung, LG, Sharp, & Sony would be my recommendations to stick to.. My personal bests? That'd be Samsung & LG. I find both their proprietary OSes (Tizen & WebOS) quite good. With TVs, your primary aim should always be their DP first, then the OS, UI, apps store, connectivity, etc.. Get one that officially supports Netflix & YouTube up to 4K UHD at least. HDR all is optional depending on your budget. I would steer clear of the Android OS powered ones. Unless you are getting the high end models. Top of the line stuff, as manufacturers would release a more stable firmware for such and maintain it longer. Got many good and cheap external boxes you can upgrade every year if you want. TVs? that's an expensive hobby.. 
Too many to recommend. Question is finding the service that satisfies you and them to run on the box.. See my signature, all the boxes I've reviewed are decent ones and should handle fine. Pick your poison.
Yeah...legally? Sticking with Asterruk is ideal.. However, that freeview package is a joke for those who have already experienced Asterruk channels..It's akin to downsizing from a luxury bungalow to a tiny apartment. 
See my signature, all the boxes I've reviewed are decent ones and should handle fine. Pick your poison. As for lag, network lag will depend on your network performance and that of the server being connected to.