Hi,
You've quickly discovered the current limitation to the cluster feature.
When adding objects, they need to be added for every computer. Also, you don't need to add a separate viewpoint for each computer. You can use one viewpoint, just set the mask to a different client when changing the viewpoint. So try changing your code to the following:
Code:
viewpoint = viz.get(viz.MAIN_VIEWPOINT)
viz.clustermask(viz.CLIENT1)
viz.windowsize(320,240)
##viz.clusteroffset(30,0,0)
#viewpoint.rotate(0,1,0,20)
viewpoint.translate(0,0,-4)
viz.clustermask(viz.ALLCLIENTS)