Hey,
this is what I had found out.
I am using two control boards so in theory it should work for all others as well.
I had the same headache as many others not being able to get player two working. I worked on it alllll Christmas long, until I hit the snag.
I went to the setting to fully factory reset recalbox, this cleared out everything with the controllers for me. I also only configured player one and co figured hotkey only for player one.
It worked that way, then I realized the joystick for player two was backwards, I just turned that joystick around in the panel and it worked perfect.
Solution = only configure player one all others should fallow. Then make sure every single button, and joystick matches the very same slots as player one.
For instance if you connect one button in one slot every single player after that must have the same slot with the same botton.
If you have a two button cab, then you hook the closest button to you to the first port, you must do the same with the other control board as well.
I found this video which helped greatly.
https://youtu.be/tRm3cVw4NcM
