Welcome to the forums Frasc0. Nice spoiler warning you have there.
I don't recall my Greycloak count ever dropping whilst playing NWN2. If it is constantly dropping everytime you speak to Kana (i.e. keep time progresses), then the most probable answer is a bug. This is fixable, I can provide a solution if you wish. But it might sound like cheating.
Here's the solution, I wrapped in it spoiler tags, so highlight to read.
Go to your golbals.xml document in your current save game file. I recommend backing it up before modifying anything. It is quite long, but scroll down until you see the code 21_Num_Recruited. It has a value behind it. Changing that would effectively change the number of Greycloak recruits you have.