Before you go any further, set aside 10 minutes to pray to Cthulhu for a swift end. Wear a lot of black and begin by lamenting humankind’s failure to accept the inevitable.
Ok, with the preparations out of the way…
Most of those, to me, sound like they have several layered “drones”. There’s usually a mid-range component and a whistle or wind-like component. The mid-range ones have more complex oscillations: wavetables, looped industrial machine samples, ever-so-slightly-detuned dual or triple analog oscilators, maybe some FM… something to make texture. The whistles might have a significant white or pink noise component, and have sharper resonant filters with moving cut-off. Play both into the same compressor and reverb/delay for the impression of being “one sound”.
One or two of your examples have a vocal-like quality. Dig out/make some choral samples and slow them down for an eerie ritualistic impression. Band-pass and bit crush them to make them sound distant and inhuman.
If you can get hold of an MS-20 or software clone, the filter on that is great for “screaming”, but failing that any resonant filter fed into a distortion should get you somewhere entertainingly unsettling.
Add a lower-still “rumble” layer with shifting low-pass filter, but consider ducking it with a compressor side-chain keyed to the kick.
Use two or three of the same kind of sound, but processed slightly differently for more pressure. Especially good in the mid-range.
(Remember to close the session off with a banishing ritual. You want the end swift and painless, but not so soon that you don’t finish the track off)
