Hi, Cathrine,
NW is also enhance by Earth colors, so if you use an Earch color to support the SW direction it will also enhance the NW as metal is enhanced by earth.
What's the cure suggested for your 20 year illness star according to the chart? Maybe your illness star will be enhanced by earth?
With respect to my children, I used their elements and colors in their rooms, but I gave priority to the Time Feng Shui suggstions.
Regarding colors, I use the quantum colors in my bedroom but I only activate one or tow color pairs at a time, depending on what I want to achieve...
I know sometimes it not easy to make a good choice, but have you already tried muscle testing? It could really help with your decisions...
Love,
Astrid