Hi Tim,
Admittedly, it is difficult to follow the workflow. Have you considered where the center pivot is on each of the objects, including the group node. That is important. Also, you may need to "group the group" in order to provide a free node for the transformations that will occur between the overall head constraints and the eyeball group. Do you know how to change the pivot point? (just toggle on the "insert" key to move the pivot point on any node, make the adjustment and toggle off the insert to get out of component mode). Are you rigid binding the eyeball to a joint that is in the location of the eyeball group? I think that the problems that you are encountering have to do with the grouping issues though. Hang in there. I know that it can get frustrating.