Here is my AP1600 quad scope rig.
One 250 mm RC scope
One 152 mm refractor
Two 80 mm guide scopes.
Two through the mount power lines each feeding a ten-port Rigrunner power distribution unit.
One through the mount power line from a separate power supply for the anti-dew system.
Two through the mount USB cables each feeding a seven-port Startech powered USB hub.
I also added a USB controlled relay box on the mount to allow me to power cycle old school USB cameras and filter wheels.
The mount has its own power supply and is connected with an old reliable RS 232 line.
All of the off mount equipment is housed in a waterproof cabinet, and AC power is controlled with a WiFi DataLoggers switching unit.
All acquisition software, including APCC, SkyX, PHD2, Focus Lynx Commander, SGP, PEM Pro and MaximDL runs on a Kingdel industrial computer. There is a field monitor in the cabinet, but normally the Kingdel runs headless and is controlled from various computers using Remote Desktop.
With the help of APPM, I have no difficulty getting round stars with eccentricity of .5 or less, as measured by PixInsight, in either of the main scopes using either of the guide scopes.
I regularly image with both scopes, one camera shooting automated sequences controlled by SGP and one controlled manually with SkyX to work around dithering.
A key to successful side by side operation is to only use the best saddles, rails and side by side bars. No el cheapo. The target is visible in my main and guide cameras.
It takes careful balance to make it all work, and avoid off center loads.