Not sure if it's the same for Android, but I think it is.
For my iPad/iPhone I have a DJ! splitter connector like this:https://www.digitaldjtips.com/2013/02/u ... a-keyring/
and also in my DJ cable gear I have one of these:https://griffintechnology.com/us/dj-cable
These are, as said, DJ splitter cables.
They take the left output from the headphone socket and translate that to false stereo (is mono but on both channels) in one output and does the same with the right output. So you end up with two different mono signals coming out of the outputs, yet in L+R, so both speakers or sides of a headphone have sound (again mono).
Clearly if the software allows you to set the output to deck 1 / deck 2 output for use with external mixer, you'll get that as output instead of main/headphones.
You run 3.5mm to stereo rca cables from the splitter to both mixer channels and off you go.
Any other kind of splitter won't work as it's wired in a different fashion.
Hope that helps some. Just my 2 cents as usual.