As a general rule of secrecy, anything witnessed by more than one person is public. If not immediately, someday.
The contingent was not large, also sort of all sworn by blood oath, I suspect. In their minds, they could have felt like kindred. I hope one of them does blow the cover if that is the case, especially if money is to be made in the deal.
It was so important they forcibly kept outsiders away to be locked in secret with their victim. I really still think it was an occult ritual.