The Heralds of the Unspoken are the clergy in the underground city in the silent halls and those soulless attendees in the arena. When I kill them, I get the faction messages:
Your faction standing with Heralds of the Unspoken got worse.
Your faction standing with Forsaken Believers could not possibly get any better.
Your faction standing with The Conscripted got better.
I am still dubious to heralds at this point due to previous faction work. I then go to the Forsaken Village and kill the forsaken there, after killing 5 of them my faction is maxxed again with heralds ( still dubious) and I am still dubious with forsaken. this is how I am building up to max ally with conscripted and will remain non kos to both heralds and forsaken