>>499149372This. As you mentioned, Bandai Namco's website states that "this foul covenant snuffed out the lives of many of the God-Queen’s kin throughout the empire, too numerous and too scattered for her godly protection to save".
Ranni was the one who stole a fragment the Rune of Death, most likely with help from Marika.
The Black Knife Assassins were rumored to be Numen with close ties to Marika.
The echo of Marika's words that Melina at the Capital Outskirts is directed to "her children beloved", and tells them that should they fail to become aught at all they'll be forsaken and amount only to sacrifices.
There's a ghost NPC that calls the demigod in one of the Walking Mausoleums Marika's unwanted child.
The Mausoleum Surcoat mentions that the mausoleum bell rings in constant mourning of the soulless demigods.
Lhutel the Headless sacrificed her life to protect a soulless demigod in Death until their revival.
The Eclipse Crest Greatshield dropped from Mausoleum Knights mentions that the eclipsed sun is the protective star of the soulless demigods and aids the Mausoleum Knights by keeping Destined Death at bay.
The Eclipse Crest Heater Shield mentions that the sun in eclipse is said to be the symbol of the Wandering Mausoleum where the soulless demigods slumber.
A Finger Reader Crone mentions that Godwyn should have died a true death, as the first of the demigods to die, as a martyr to Destined Death.
Black Knife Tiche was killed protecting her mother during their flight from the royal capital.
There are many things I still don't know about this night, but from this I'll conclude that the demigods in the Wandering Mausoleums were slain during the Night of the Black Knives, after Godwyn's death. This fits with their soulless status, needing protection from Destined Death, and the website's description of the events.