Why do you need a differential op-amp at all?
You are using a PIC with analogue inputs, let the PIC calculate the difference between the two voltages and drive the BFY50 accordingly.
Or am I missing something?
Also there is a mistake in your circuit as drawn, pin 12 of the PIC is connected to +5v and the second LDR is shorted out.
Also, the two relays could be replaced by one double pole relay, or driven from the same transistor. (Unless you intend to short out the motor to give dynamic braking).
JimB