Here are a couple screen shots showing Set List Maker running in an iPad Pro simulator, sharing the screen with Safari for copying and pasting lyrics. You could open a mixer or effects app there instead.
Split screen apps can use 1/2 of the screen or 3/4 of the screen, with a second app in the remaining 1/2 or 1/4. When Set List Maker or BandHelper are using 3/4 of the screen on an iPad Air or iPad Mini in landscape, or 1/2 or 3/4 of the screen on an iPad Pro in landscape, they will use the two-column iPad layout. When they are using 1/2 of the screen on an iPad Air or iPad Mini in landscape, or any configuration in portrait, they will use the one-column iPhone layout.
If you plan to use shows (set lists) in split view, you will need to adjust your layouts or add new layouts for the non-standard window sizes used in split view.