I have AWS ECS cluster with with one instance.
This instance has four containers (2 staging, 2 production):
How can I create a second instance and move two containers production to new instances?
Why you've chosen to have such setup for staging and production environment ? If something goes wrong in staging container, production also will be affected.
Create 2 Clusters and 2 Fargate Tasks, for staging environment to be used staging image and for production the production one.
Don't build monolithic things ….