Try this
SELECT
login_user,
right_left,
sponsered_id
FROM (
SELECT
login_user,
right_left,
sponsered_id
FROM
members_list
UNION
SELECT
NULL,
CASE when max(right_left) ='Left' THEN 'Right' ELSE 'Left' END AS right_left,
sponsered_id
FROM
members_list
GROUP BY
sponsered_id
HAVING count(sponsered_id) < 2
) as temp
ORDER BY
sponsered_id,
right_left