I ordered some of the 4N38's that AnalogKid recommended. I suppose these will work the same way as the PS2501-1's. I will give it a shot when they arrive.You might consider PC2501-1. 4 of these individual opto pairs will stack in the same 16 pin DIP pattern the -4s do.
Again I just want to be certain. I know you already explained it, but after the inverter logic, would you suggest using another opto to eliminate a voltage onto the ground of the DEK Phoenix relay? This would just closed the logic and complete the circuit