It is noted that the combination of mountain star 5 and water star 9 or the reverse is not a good star combination as they bring bad luck. So, what are the remedies to improve the feng shui of a master bedroom/living room/main door if these stars reside there?

Hi Dan, the star 9 is 'future prosperous'. As a Facing Star 9, it makes a good main door or living room. As a Sitting Star 9, it makes a good bedroom. When you use the star 9 appropriately - let's say door at Facing star 9 - the Sitting Star 5 would be useless already. Similarly, when you sleep in a Sitting Star 9, the Facing 5 will be off. Sitting and Facing stars are opposite. That being said, the 5 is only 'negative' when provoked by external features. If not, every house in a same row will be affected. Last but not least, star 5 has its own uses too ... Cheers! SN