The only way to create a graph with multiple VMs is to create a static membership to the graph ( self provider on) and add in the individual VMs and the metrics you want at the bottom
There is no way to use a metric configuration file and select a group of VMs from an object list and see the VMs listed in the graph (the graph widget does not have the Parent Self Child selection list) Also you cant select multiple VMs from an object list and do the multiple insertion into the graph either.
I have been asking for this function for 3 years now. I hope they add it in some time soon. Chart widget is great for getting lots of metrics for one VM but not one metric for lots of VMs