If you look at the underside of those two problem keys compared to those on the keyboard you'll see that they're mounted on round stems instead of flat bars to facilitate their removal. In your last photo it appears that a part of a threaded section below the key is visible, so your hunch that they need to be unscrewed is most likely correct .  

I would carefully support the stem with needlenose pliers to prevent it from being twisted (grab it as low as possible and use a piece of cloth so that the plating doesn't get damaged), and then try to unscrew the key in a counterclockwise direction. It's possible that the threads are slightly corroded, so a little bit of penetrating oil (WD-40) concentrated in that spot should help. Just cover the rest of the machine with a rag before you spray or you'll have more of a mess to clean up later on.

I have the noiseless model that preceded and succeeded yours, and neither have that set up, so I wonder if it was a problematic arrangement? Since I don't own your exact model, please triple check the connection point underneath the key for any sign that the key and stem are in fact two pieces before trying to unscrew them.

Good luck! 

I almost had a heart attack when I saw your first photo because it looked like you had snapped the top of the stem off! 

Glad it worked out for you though. Whenever I tackle something new, or don't fully understand how it works, I usually try to look at the problem from every possible angle before bringing out the tools. Forty years ago we could have afforded to take a more devil be damned approach to repairing machines, knowing that replacement parts are a phone call away provides a nice safety net, but now we have to be extra careful to preserve the parts we have.

Anyway, enjoy the machine and hopefully you'll feel inspired to share some photos of your other machines in our photo gallery threads. 

Yeah!! that one had me going too!!  And I've snapped off alot of parts in my time.  Usually I've been able to fix them back, and in this case, it looks like roll pins have been used.  Quite cleaver!!  Think I'll remember this if and when I run into a similar problem.  Thank you.