Approach the solution differently.
Instead of trying to use different service accounts, use one service account that has access (privileges) to each project.
Create a service account (or use the one that you created). Make note of the service account email address (this is its ID).
Go to IAM for each project and add this email address as a member. Assign the roles/ permissions that you want for this service account. Repeat for each project.
Now you can use this service account json file to setup gcloud, software applications, etc. All you need to do is specify the project when using the credentials.
gcloud auth activate-service-account firstname.lastname@example.org --key-file=test_google_account.json
You can set the default project with
gcloud config set project PROJECT_ID. Or use the environment variable
You can specify the project on the command line with
gcloud --project development-123456 compute instances list