Only front one only. Even if the resolution is (1920+1920+1920)x1080, the pixel is still square.
Thanks to vFOV logic, there's no unexpected zooming in/out.
Or you're talking about completely different rendering, not linked to the forward field of view? Like forward uses different FOVs, and "left" and "right" are strictly "to the left" and "to the right", and there's a possible gap between "left" and "front" as well as between "right" and "front"? I remember 1993 year DOOM had "-left" and "-right" switches allowing to use three computers to render left, front and right views.
If the latter, you want to use additional monitors as side windows for your cockpit? Well, it's an interesting feature you're asking for.
Well, the simple way to do that is just repeat each rendering command (with different camera transformation matrix settings) for each of rendering targets. And there're some minor problems, like putting night goggles ellipse on the resulted scene, or text messages. But yes, it's solvable.
Please provide more details about how you see the feature, connected with questions of changeable FOV and moving game head. Couple of "top-down" field of view drawings may help.