I personally believe that sithis is not sentient or self aware and here is the thing I believe that the night mother is actually mephala or an aspect of her they call the night mother Mephala in daggerfall and there is a book that talks about the split with the tong.
All the night mother does in the dark brotherhood fits Mephala's sphere of influence looking at oblivion how the night mother just sat by and allowed the betrayal and the infighting to run its course.
All of the contracts of skyrim deals with mephala's sphere as well.
After looking at everything it just points to it being her I can't see it any other way
plus sithis can't have children it makes no sense what so ever.
What do you lore buffs think? You know more than me so I want to see what you think about all of this? Does the dark brotherhood know that the night mother is Mephala? Or have they simply forgotten? Or is this all a game in Mephala's web? The original split and all the issues that have plagued the tong and the brotherhood is it all of Mephala's doing?