No, it is not possible to restrict participants within your domain to accept external users' join requests (e.g: disable students from accepting external requests isn’t possible). We’re working on giving more control to meeting owners. Follow this article to keep yourself updated.

Students will not be able to re-join a meeting after the final participant has left if:

• The meeting was created using a short link like g.co/meet/nickname
• The meeting was created at meet.google.com by entering a meeting nickname in the 'Join or start a meeting' field
• The meeting was created in the Meet app by entering a nickname in the 'Meeting code' field
• This means that if the teacher is the last person to leave these types of meetings, students cannot join later without the teacher. This feature has started rolling out and should be available to customers within 2-3 weeks.
   

Yes, it is possible to disable meeting creation for students. The way this can be achieved is by enabling 'Meet video calling' only for the teacher's organizational unit. By doing so, only teachers will be able to create meetings while students will only be able to join the created meetings. Visit this article for detailed steps on how to disable meeting creation for students.

No, it is not possible for an external participant to join a live stream from your organization.

Yes, this is a recently rolled out feature. In case this isn't available on your account already, it will become available in the next 1-2 weeks.

No, it is not possible to change your background in a video meet at this moment.