Whether or not you should create an account for each person in your group primarily depends on whether you're going to take lessons individually or together.
If You Are Going to Take Lessons Together, as a Group
In this case, just having one single account is the best idea. There's no need for multiple accounts if you plan on taking lessons together.
If You Are Going to Take Lessons Individually (or you might in the future)
In this case, we recommend creating separate accounts for each person in your group. This allows your teacher to easily take notes on each student separately, which is important. You can purchase lessons in one account and share them so all the other accounts use them; read here on how to do that!