Yes, it's possible. I have two 4k monitors, one in portrait mode. For a long time I ran them at 3840x2160 and 1080x1920. Now I'm running them both at 4k (3840x2160 at 60fps and 2160x3840 at 30fps).
I'm not using "fullscreen" or "fake fullscreen."
When I previously tried to have 3D graphics on both monitors at 4k, it wasn't working smoothly. Now, my second monitor shows only the "cartographic map" so there are no 3D graphics on that monitor. That might be why everything is working out for me.
To be clear, I was always able to display the game on two monitors. But it ran choppy or something which is why I dropped the resolution.
Can I ask how your two satellite monitors are connected to your computer? E.g. is this an office machine where extra monitors are attached through USB cables? Are they plugged in with DVI cables directly to your graphics card? It sounds like the problem is that the game is not recognizing that a second monitor even exists.
One possible workaround is to use "fake fullscreen" with "ui-festival." You could set the resolution to 3200x1080, which would spread your game across 2 monitors. Then you use settings in "ui-festival" (which you can edit while the game is running, or by editing the game prefs file) to set the "SplitRatio" to exactly 60 (60%).
I think if you use fake fullscreen, then it might not matter whether the game recognizes your 2nd monitor. It would be sufficient that Windows 10 recognizes the second monitor. That's just a hunch I have.
Here is a link to the "Fake Fullscreen" instructions: https://forum.faforever.com/topic/123/guide-fake-fullscreen-and-optimisation