Do not try to set up a player 1 and player 2 using the index method in some posts here, that is when my controls quit working.

Edit the configuration file below for only 1 player. It seems player 2 gets duplicated to the exact button layout. Make sure your button wiring for both controllers are mirrored copies of each other.

input_device = "THT THT Arcade console 2P USB Player"
input_driver = "udev"

#Player 1&2P

input_b_btn = "1"
input_y_btn = "0"
input_select_btn = "8"
input_start_btn = "9"
input_up_axis = "-1"
input_down_axis = "+1"
input_left_axis = "-0"
input_right_axis = "+0"
input_a_btn = "3"
input_x_btn = "2"
input_l_btn = "4"
input_r_btn = "5"

input_enable_hotkey_btn = "9"
input_exit_emulator_btn = "8"

Put the edited file in /opt/retropie/emulators/retroarch/configs named THTTHTArcadeconsole2PUSBPlayer.cfg, for some reason the Xin MO gets named that.

Hope this helps.