DirecTV Stream and additional Directv streaming boxes

I have had an a streaming account for over a year. I currently use a Directv streaming box.  I have a second directv streaming box and would like to add a second TV to my home.  With the current changes with DIrecTV, i.e. adding DirecTV via Internet along with DirecTV stream, I am unsure if I can add the second box which I think is now called the Gemini without additional monthly charges/fees.  DirecTV says one can Bring Your Own Device but doesn't say if that can be another "Gemini".  I do not want to loose my Stream account nor do I want to incur any additional fees.  Please advise whether I can add the additional 'Gemini" and not be charged anything extra than what I'm paying now.  This will affect whether I add the second TV to my home.   Thanks