You have one GCP account running in your default region and zone and another account...

"Run gcloud configurations list to start the Compute Engine instances". How the heck are you expecting to "start" GCE instances doing "configuration list".

Each gcloud configuration has a 1 to 1 relationship with the region (if a region is defined). Since we have two different regions, we would need to create two separate configurations using gcloud config configurations create

Ref: https://cloud.google.com/sdk/gcloud/reference/config/configurations/create

Secondly, you can activate each configuration independently by running gcloud config configurations activate [NAME]

Ref: https://cloud.google.com/sdk/gcloud/reference/config/configurations/activate

Finally, while each configuration is active, you can run the gcloud compute instances start [NAME] command to start the instance in the configurations region.

https://cloud.google.com/sdk/gcloud/reference/compute/instances/start