Subscribe by email for entire multisite blog

We have an educational multisite blog that has the main site – and then, eventually, there will be 12 blogs under it as sub-directory blogs for each element or what we call a Journey. So, it will be….12. I have installed subscribe by email in the hopes that they could enter their subscription once and get notified of new posts for the entire set of blogs.

So, if they enter their subscription on Journey1 it will notify them if there is a post on the .com blog or Journey2 blog, etc. Is there a way to configure subscribe by email to do this? Or, is there a way I can import my subscribers from one blog to another.