A multi-instance StackPack requires a provisioning script that's able to provision multiple StackPack instances. To achieve that, you need a separate template file in the context for both stackPack and instance; stackPack needs to be provided with the shared-template.stj, and instance requires the instance-template.stj as in the example below:
Note that instance-template.stj has some instance specific information, like topicName, instanceId and anything else defined in templateArguments, while shared-template passes without any specifics ([:]).