Are you able to clone those monitors together using the Windows display settings? If not, DisplayFusion won't be able to either. Windows has some limitations on what monitor can be cloned

You could try setting them to extended and use the "Mirror Monitor" function (set a hotkey on it on the DisplayFusion Settings > Functions tab). It will mirror a monitor to a new window that you can drag over to another extended monitor. It's not suitable for fast moving stuff like video or games though.