Hi,
So from what I understood you intend to control Machine 1 when the relay is ON and Machine 2 when relay is OFF. Also all the 24 signals are from 24 individual pins right?

Exactly

 

Also what is the voltage & type of signals are those 24 signals? The 4 channel 5V relay you have shown as example above I think the input pins IN1, IN2 etc should have around 1-5V signal and power +5V and GND