from the Dark angels background info in their most recent 40K codex.
The inner circle is composed of the Deathwing, all of the Masters (company captains), the grand master (head librarian) and the supreme grand master (chapter master).
The deathwing is composed of the first company (terminator vets), the interrogator chaplains, the senior librarians, the master of the forge, and most of the chapter's landraiders.
Librarians are not informed of the truth upon induction, but upon being raised to senior librarian, and only raised after discerning part of the truth themselves.
there might be some inaccuracy, particularly on the tech-marines, and i don't know about the apothecaries, since I am writing from memory, but i am certain of the last point.