@davindersangha I made a similar attempt where I wanted to have two active joy sticks on one game This just won't work. Can't set two controllers as player 1 or two. Can't have multiple active controllers for player 1 type thing. But..... If you got a very compact and mounted it under the switch so the switch hit the 1 button which is start that could work. Or just mount the keyboard on the chassis and use the 1 / 2 for one and two players. The keyboard always works in tandem with the controllers.
Please do not post a support request without first reading and following the advice in https://retropie.org.uk/forum/topic/3/read-this-first