If you are trying to get rid of ground problems, you can, obviously, use optocouplers. I would, however, get rid of the ground problems first. Even with optocouplers something strange can happen when the ground floats. Once you have gotten rid of the ground problems you can install optocouplers as a safety.

FIRST add a ground wire to your circuit, the lil' ol' black cube on the wall probably does not have ground and your circuit MUST have that to conform. I believe that will make your problems magically disappear.

Erik