If you are the admin, then you can view all the jobs that are opened by you as well as by other managers in the team and schedule interviews for any job. If you are a manager, then you can only view the jobs that you have opened and schedule interviews for them.

If the interviewer is already a team member, then you will see the interviewer's name in the drop-down list in the "Setup new interview".

You can add a new interviewer by typing the interviewer's email and on clicking enter, the option to enter interviewer's name shows up.