Step 1: The Solution
But the remote may be still too complicated for them. And the answer is....
Step 2: Highlight the Useful Buttons Only.
The remote in the picture is laid out pretty nicely, but it can still use some improvement. We can do one of many things:
1) Open the case and physically slice off all the rubber buttons users do not really need. (I have not chosen this step, but it should be pretty obvious. An X-Acto knife should to the trick. Be careful using it.) You can then cover the holes with plastic sheet.
2) Highlight the useful buttons by painting them a bright color and redrawing the button icon, or by drawing around the button with a bright colored ink.
3) The easy way out: Obliterate any buttons that are of little use by painting over them. A sharpie marker should do fine.
So, the pictures in this step show different cases of obliteration, following solution 3. Personally, I do not have a need for such a remote, so I am demonstrating the solution by drawing on the picture instead. I hope you will forgive me for this.
One note on the code search key: You can leave it in, if your favorite senior still needs to search for codes when they buy new stuff. But, even if you choose solution 3, this option still leaves the "bad" keys functional, so if you think you will need them at some point, keep a copy of their position. The code search key can still be used (by you, for example, helping your senior with a new piece of gear).