Lines of Phiarlan and Thuranni

Are Phiarlan and Thuranni elves still considered Aereni? Are they eligible to become spirit idols or deathless? What about the elves with the Mark of Shadow who serve with the Cairdal Blades in Aerenal?
“Aereni” is a culture; being Aereni means that you honor your ancestors, give your devotion to the Undying Court, and serve the Sibling Kings. The shadow-marked families — Tialaen, Shol, Ellorrenthi, Paelion, Thuranni — were never actually Aereni; they remained independent from the Undying Court, the line of Vol, and the Tairnadal, and travelled between communities of all of these cultures. When the Undying Court eradicated the line of Vol and exiled its allies, the shadow-marked families chose to leave with them. Some feared that they too would be persecuted for their marks; others believed that the supporters of the Undying Court had committed an unforgivable sin in spilling so much elven blood. As this article says, “to mark their departure from elven society, (the shadow-marked families) formally joined their lines into a new alliance: House Phiarlan.“
As for those shadow-marked elves who are occasionally seen in the Cairdal Blades? This is also explained by “A handful remained, believing that it was their duty to the kingdom; these elves found themselves largely absorbed into other lines, and this mingling of blood causes the Mark of Shadows to occasionally appear in Aerenal.” The elves who develop the Mark of Shadow in Aerenal aren’t Phiarlan or Thuranni; they are now Jhaelian or Mendyrian. And the mark only appears rarely because, unlike the houses, the Aereni aren’t trying to arrange matches to produce the mark; the marked bloodlines are heavily diluted.
So no: the elves of House Thuranni and Phiarlan aren’t Aereni. They intentionally severed their ties to their homeland and have no loyalty to the Undying Court or the Sibling Kings. And since elevation to the Undying Court — whether as a spirit idol or as one of the deathless — is an honor the Aereni bestow on their most celebrated citizens, it is not offered to those elves who have abandoned their homeland and its traditions.
With that said, a Phiarlan elf could return to Aerenal, abandoning the house and embracing the Aereni traditions; they’d just have to find a noble line willing to adopt them, just like the shadow-marked elves who stayed behind when the Phiarlans originally left. And as Aereni, such elves would be eligible to join the Court, though again, they’d have to impress the priests and people with their worth. But joining the court isn’t about whether you have a dragonmark; it’s whether you are a devotee of the Undying Court who has proven yourself worthy to join it, and whose talents and achievements justify this gift.