Do the photocouplers on this module have any possible purpose?
If you use an isolated 12VDC supply for the relays the optoisolators will help keep transients away from the circuit driving the LED side. 

If you connect the grounds, they won't do much of value. 

The transients I am referring to are coupled from the loads being switched to the coil. Relays do not provide perfect isolation, especially to fast-switching high voltage transients. Cheap crappy relays like those ones, probably worse than most.