Keep in mind that VoiceComputer does not support 4 monitors, we only support 3.
Second, if you click on the desktop on monitor one, and say "create overlay", it will span all of your monitors. However, you need to make sure that whatever application you want to create an overlay for on any given monitor must be open on such.
Third, "My InTags" (overlays) fix the size of the selected screens/applications. So, when you number your application, it will put it up on the second or third monitor in the size that you originally specified. I don't usually use that approach because I do it by application, which always keeps the application size the same as when I create the overlay. However, if you overlay the desktop area on all your monitors and then number an application or window, the next time you open that application it may not be sized correctly for the numbers that you create because the overlay is covering the entire desktop. So, I seldom create overlays except in a specific application on specific monitor so that I can always ensure that the numbers line up correctly.
You can try doing what Phil suggests, but just keep in mind how overlays work.