SELECT u.id, u.firstname,u.lastname,u.email FROM mdl_role_assignments rs INNER JOIN mdl_user u ON u.id=rs.userid INNER JOIN mdl_context e ON rs.contextid=e.id WHERE e.contextlevel=50 AND rs.roleid=3 AND e.instanceid=?Passe o parâmetro id do curso em e.instanceid=?
Caso o tutor não for id 3, altere isso rs.roleid=3