While I like the idea of a faction that can’t kill (it is much more fun to be converted than murdered) the current brotherhood is not good enough in my opinion to be put in the game.
I do think that the final form of the brotherhood (as determined in balance by FoL) would be a great addition to the game.
Also, I would like to mention a problem with the Marshall.
I was Marshall, the next day prince acted susp so we put him on trial, he claimed prince, and evil king decided his fate. I then had 2 uses abilities, with 3 uses each.
Granted, journal reading is very powerful.
I still think, however, that the Marshall’s 2 prince related abilities should be changed (to something less powerful) upon the prince’s death. Maybe listen to psychic conversation.
Brotherhood needs some minor changes, but none that it would screw over the game entirely. I thought the BH was very good in that SFoL game imo. (Quick grammar edit 
)
