Thank you, ***** ***** do help.
Swimming pools can symbolize a family unit, and they are entering in to that with their diamond. This in itself can show they will or are banding together to form a unit against you, in other words gather as much as they can in a whole to come against you.
And then in the key part of the dream when they held up the diamond for inspection and it was fake, the part you knew was important, as it is, can show that in the end when the light shines it was all a indeed a fake diamond, its was all a farce.
Consider a ulterior motive on their part, they may be trying to get something that is not in the obvious move against you, there may be something behind the scenes.
It won't work though regardless, it just may clue you in as to what is really behind their motives and help you understand, therefore guiding your actions and decisions.
So, your dream looks to be letting you know the ending of this whole circumstance will be in your favor, not in theirs. A very good dream, and great job of picking up on the key component!
Let me know if you have any questions or comments, happy to help, thank you.