Rotating GameObject problem

You have to write 2 different scripts: One to rotate the entire system, and one to rotate each individual coin. You could call them RotateCoinScript and RotateCoinSystemScript.

RotateCoinSystemScript would have an Update method that calls this:

     float rotationSpeed = 10;
     transform.RotateAroundLocal(Vector3.up, Time.deltaTime * rotationSpeed);

And RotateCoinSystemScript would have an Update method that calls this:

     float rotationSpeed = 10;
     transform.RotateAroundLocal(Vector3.forward, Time.deltaTime * rotationSpeed);

Then you add the RotateCoinScript to each coin (so they each have their own individual instance of it), and then the RotateCoinSystemScript to the parent object (what you call the "Over-Object").

You can adjust the rotation speed as you see fit. Note that Vector3.up is short-hand for the y vector, and Vector3.forward is the z vector. These are globally static properties that always return (0,1,0) and (0,0,1) respectively, but their use becomes local to the objects when using transform.RotateAround*Local* (as opposed to just transform.RotateAround).