Good adventure with some solid and fun themes. I especially love the ancestor stones. Anything where the players are given meaningful options is great. Destroy the heads to keep from being watched? Cool. The BBEG is stronger. Love it.
The only critique I have is that you can almost always eschew the word "will" and change the sentence to the present-tense. "There is a 2-in-6 chance 2 shadow specters emerge from the archway..."
I routinely have to CTRL+F for "will" because it comes natural for me to type, but it's almost always an unnecessary word *especially* in stat blocks. "Uses cultists as living shields..." and the present-tense is always stronger when it makes sense to use.
But that's really my only critique. Cool, evocative adventure.