What about the stuff about U-Olga being an alien?
That's going with the fact if she's an Alien at all which is why the story explicitly swings against it with how hard it tries to hide it's identity from the Crypters which an Alien would have no reason to.
This ALSO goes with the fact that Olga Marie was dumped into CHALDEAS by Lev, which is all but stated to be connected to the very Soul of the Planet itself.
Like isn't Holmes supposed to be the apostle of other of Olga's species?
No, that's Younger Moriarty. Sherlock Holmes is explicitly the First Apostle that was tasked to help deal with Goetia and lay the groundwork to sabotage Chaldeas. Holmes had no problems with the former but hated the latter and explicitly erased his memories of it(Which is why he's constantly wishy-washy on if he's alive or not since his smart intellect WILL find out what he did).
Young Moriarty is the Apostle of the Foreign Planet meant to stop U-Olga Marie but again, we have no idea of what Planet they are talking about and Subject E is kinda implied in Moonlight Lostroom to BE Olga Marie(Which again, doesn't make her an alien in the fashion we are accustomed to).
Does that mean that Marisbury somehow turned her into an alien or something?
No, Aliens would have no reason to hide their identity as it was stated in Lostbelt 5.2. The Trees of Emptiness can explicitly be analyzed but Sefar, a true Alien, explicitly couldn't.
Again, the common consensus is that there is no real alien attack or anything happening here and like I said before, it's heavily implied Marisbury made Olga Marie into a Beast Candidate for his own ends.
Why? We have no fucking idea.