hmmm... don't have much experience with rigging, but if the problem is with the way the head and neck joints are moving, i think it's because you have a double transformation working on them which means that they are being moved twice - i think it's because you have them grouped and so they are being moved as individual units and as part of a group - hence the fact that they are moving twice the distance as everything else. As i said am a bit sketchy on this sort of stuff and don't fully understand it, but I think that's what's happening.