I think you would need to get each workflow cluster PK for all child workflows and then set the status for each one. You are only referencing the current workflow through si.WorkflowClusterPk.ProfileKey so that is the one that is completing. I have not used this but there is a BRAPI call BRApi.Workflow.Metadata.GetRelatives which could get all the base input workflows and then you can loop through them and set the status. If that doesn't work, you may have to pull each one individually using the hardcoded name of each one.
