Origin of the Grunt and Brute and Daniel's Awareness of Them (SPOILERS)

[MPS626]

Spoilers: I discuss events up to the Choir, Chastel, and Transept, not with too much detail. (Sorry, I'm new to the board, don't know how to do the hide spoiler button thing.)

Alright, I've played through myself once, watched two separate playthroughs, and read most of the diary entries/flashback transcripts/notes online as well as in-game. I still can't quite understand how the monsters came to be. One theory that everyone seems to accept is that Wilhelm and his men who were locked in the wine cellar are examples of how Alexander created the Grunts and/or Brutes, but here is my problem with that:

1. Daniel tries to get into wine cellar, door is locked.
2. Goes to study, finds key and note titled 'Regarding the Closing of the Wine Cellar'
3. Goes to Wine Cellar, finds no other entrance or exit and mutilated body parts.

To me, the game implied that Wilhelm and his men really did die in the wine cellar as Wilhelm said they would, since if Alexander was going to make them into the monsters, why would he need to lock them inside since it would make them loyal to him once they were transformed (i.e. even if they escaped and ran outside, they'd eventually be turned into monsters and return to Brennenburg). Also, if they were transformed into monsters how did they get out and into the castle since there are none (that I ever encountered, anyhow) in the Wine Cellar? I know as far as game mechanics go they can apparently disappear/respawn/teleport/what have you, but in the Guest Room monster attack when the monster left you heard a door open/close, and since the door to the room you hid in was busted down by the monster, I assumed this was the door from the Guest Room to the Back hall. This door sound and then the mutilated torso right outside the door seems to imply to me that the monsters in the game's actual world don't really teleport or respawn, and that is just the game's way of getting around difficult mechanics or animations.

Also, I'm curious about if Daniel was aware of the mutilated servants. Most people say that they're mentioned in several texts throughout the game but I would argue that Alexander also kept regular, human servants around the castle too, since in Daniel's Diary "Brennenburg 1/3" where he describes his arrival there he mentions the servants being odd but not about them being horribly deformed with hook hands, which I think he'd be a little bit more alarmed by upon first arrival than his diary seems to convey.
A few more points to this effect:
- when walking through the Refinery with Alexander (we hear their conversation in the form of a flashback before seeing what was in most cases the first Grunt of the game), I got the impression that Alexander keeps it dark in order to conceal the monsters from Daniel as they make their way to the inner sanctum
- the arsonist's screams as they take him to the torture chamber (again, flashback) say something like "you're a man, how can you do this?" It might just be him trying to appeal to Daniel's humanity but I thought I could hear some surprise in his voice on this line as if he was expecting something other than a man to be dragging him away

One more question (though I know I'm probably really overanalyzing all of this, but it's been bugging me). I know it's pretty widely accepted that the monsters are the Gatherers mentioned in the folklore, but I was confused about this since Wilhelm obviously kidnapped around 100 people while he was still fully human. I guess this just makes me unclear on how long Alexander has had the Grunts and Brutes (or 'Mr. Face's and 'Mr. Tall's, as they prefer to be known) working for them, and if they only kidnapped animals (as the folklore book implied) or people as well, and if so, why did he need Wilhelm?