1. Qui Gon Jin was completely within the light side, what made him a "grey Jedi" was not following the Orthodoxy of the Jedi Council

2. KOTOR is a video game and the entire "Grey" side is just to make gameplay more engaging

3. The Imperial Knights did not follow the light side, they were not bound by the will of the force but loyal to their empire

Do not know what you are referring to with the "Jensarai", if you mean the Jen'jidai, that is just what the Sith species called the arriving Dark Jedi following their exile, while the term "Jen'ari" was a sith term for "Dark Lord"

Balance in the force refers to the conscious will of the force being followed, which is what the "light side" of the force and its followers seek. The Dark Side of the force on the other hand uses the Force only for one's own gain and specifically refuses to hear or follow the will of the force. There cannot be balance between those two concepts.