I am working with three raspberry pi boards working for a particular task. I have programmed them such that they will all work simultaneously in different environments and the one that succeeds to complete its task, signals a stepper motor to move to a position based on the results of the program. I initially did this with a single Pi board and was successfully able to control the motor. However, with three boards working together, the motor takes no signal from any of the processors even when I have used a multiplexer (CD74HC4067). I have attached the circuit diagram below. To clarify, motor is being signalled by only one processor in a cycle.
I am from the mechanical engineering background and a novice to electronics and have learnt about the components and their working with google. Kindly consider this and pardon me if I am being stupid anywhere.