How do I create a Webform that will open a case and assign case role
I setup three contacts, all with just first and last name for simplicity sake.  Here is a screen shot of the case setup for Webform-CiviCRM 7x.4.10.    



I haven't setup an activity to also be created when the form is submitted.

When the form is submitted, it creates the client, source contact and case coordinator.  Then creates the case with the client as the client and the case coordinator as the case manager



Note that it does also create the relationship between the client and the coordinator outside the case in addition to inside the case.  The rationale here is that if the client has more than one case, it would be useful to know who the other case coordinators for that client are.  This relationship will be automatically pulled into the Other Roles fieldset of subsequent case(s).



Joseph