To send a broadcast email or email that goes out to subscribers of your sequences you would need to first create a newsletter.
When you send emails in a newsletter you are able to select the recipients from sequences, as well as any subscribers to that newsletter sequence.
Below is how you can set up your emails to send to sequence subscribers. Note - this does not show them as subscribers to the Newsletter (as they are still only subscribed to the sequence) and it would not send to anyone who has unsubscribed.