How can I share Stadia Pro subscription with my family members? I have them already set up in Stadia Family with their own account, but they cannot seem to use the Pro subscription I activated in my account.
As you have now realised, family sharing isn't a feature that is available yet on Stadia. It is a planned feature but currently not yet available, and the specifics about how it will actually work are also unknown currently.
I think the feature will be available in the future and it will be great.
At the moment, I recommend you to send a feedback to show your interest in the feature from the app.