Using a PNP transistor with Arduino to close a circuit
You need NPN transistors like this (1 channel)



PNP transistors will switch up to a positive supply and you have already stated that the controller inputs need to be grounded. 1k2 resistors are fine and virtually any NPN transistor will be fine.

A low output from the arduino does not trigger the NPN therefore it remains open circuit. A high from the arduino turns on the NPN transistor.