At a 2007 interview, the Turgor developers stated that there would be 11 Sistes and 11 Brothers, and the player would be tempted to become the 12th one.
At the cheat section, I've found that both the 11th Sister and the 11th Brother are called "Doppelgangers", but in videos of the game, as well as any information I've been able to get, there are only 10 Brothers are 10 Sisters.
Are there really those Doppelgangers in game, or are the 11th Sister and the 11th Brother and idea dropped by the developers? If yes, can we actually spawn them in the game via the console commands, or weren't they even finished?
Thank you a lot!!!

I believe one is the resurrected nameless sister. For the other - you just have to survive long enough to see him (a bit disappointing though - but it should be?).

I'm a bit confused... interviews done as little as 6 months before the release of the game do consistently state the existence of 11 brothers, plus the 12th brother which would be the player. Is any information known on that mysterious deleted brother?
Edit: I've found you can spawn a Doppleganger on the map and enter a "fight" with him, just he's there, in the middle of the Mongolfier arena, without moving. Has anyone tried to give it proper animations or intelligence? It would be a very interesting project (a friend of mine is 3D animator so if you need some help...).

Like Avimimus already said, Doppelganger is indeed included in the game, as he said just survive long enough and you find him