Ought I still buy a honing rod, if I'm buying multiple whetstones of different grits?
Maybe.

Should you have a honing steel?  Yes.  Should you use it regularly?  Yes.

Are you actually going to use it?  ... well, many people don't get in the habit of it.  And unless you're in the habit of using it regularly, it's not going to do you any good.  And well, if they're like my grandparents (before they passed), it can be a challenge to develop new habits.

Once the blade has gotten bad enough to really notice, you need to actually sharpen your knife ... but that slowly grinds down the knife, and if you're not careful, you can change the curve of the blade.

I wouldn't recommend whetstones unless you're maintaining a lot of knives.  For one knife, just go out and get it professionally sharpened.  A professional knife store will do a phenomenal job, but for most german knives, you can just take it to most kitchen stores these days and they'll just run it through an electric sharpener (the same as you might) for around $10.

But honestly, a year is rather quick for a home chef to dull a knife to the point that you're talking about.  If you're going to splurge on something, make sure that they have a good cutting board.  (plastic or wood, not glass, stone, or other ceramic.