Not sure if its the most effective way of doing it (or if it works as expected), but you could try with a subquery.
Also updated it to use aliases on the tables, less text.
SELECT sl.member_id, SUM(sl.cp) AS totalCp, SUM(sl.week_score) AS totalScore,
m.firstname, m.lastname, m.id,
(SELECT SUM(g.score) FROM `groupWinnerPrediction` AS g WHERE g.memberId = '$row[id]') AS gWinnerScore
FROM `members` AS m
LEFT JOIN scoresLeague AS sl ON m.id = sl.member_id
WHERE m.active = '1'
GROUP BY sl.member_id
ORDER BY totalScore DESC, totalCp DESC
Then to make it even harder i need to add totalScore and gWinnerScore together within the sql
Why can't you do this in php?
You should be able to do this, but i hope there is a better way ...
SELECT sl.member_id, SUM(sl.cp) AS totalCp, SUM(sl.week_score) AS totalScore,
m.firstname, m.lastname, m.id,
(SELECT SUM(g.score) FROM `groupWinnerPrediction` AS g WHERE g.memberId = '$row[id]') AS gWinnerScore,
(SELECT SUM(gw.score) FROM `groupWinnerPrediction`AS gw WHERE gw.memberId = '$row[id]')+SUM(sl.week_score) AS totalx
FROM `members` AS m
LEFT JOIN scoresLeague AS sl ON m.id = sl.member_id
WHERE m.active = '1'
GROUP BY sl.member_id
ORDER BY totalScore DESC, totalCp DESC