Being given to them by Eraqus means nothing. And why would he need to mark Ven when he already had an eye on him before the heart-splitting fiasco? Terra, Ven, Aqua, and Eraqus were all Xehanort's pawns. Even if they might have worn them voluntarily (even Riku whose clothes had "X"s on them), they are still wearing an "X".
That is how I see it. You are right that we don't know how far of a reach Xehanort had and who he exactly marked besides the Organization and Sora, but there is no coincidence in this anymore. They had "X"s on them, and they were all potential vessels for Xehanort and potential tools to create the X-Blade.
How can that mean nothing if Xehanort wasn't even involved in the whole thing? When Xehanort brought Ventus to Eraqus it was the very first time he ever
saw Aqua and Terra and they already had their straps.
He also didn't mark Ven at all after that. Even when Aqua watched over Ventus when he was still comatose and Xehanort long gone from LoD Ven still didn't have his crossing straps.
The way I see it, you are all way overthinking the whole issue. In DDD Young Xehanort never speaks in plural and only about Sora's DDD clothes. There's no real proof of everything "X" in someone's clothing suddenly being a tracking device.
It was also never said that Xehanort (or rather, Ansem SoD, as he was the one who did it) "marked"
anyone besides Sora in DDD, not the Organisation or anyone of TAV. As far as I remember the black Org coats have nowhere an "X" so the first Organisation wasn't marked at all and Roxas already had that "X"-zipper when he was
born, before Xemnas even found him.
And what do "sole creators" become? Eternal. Gods. Gods are beyond life and death by our definition. Omniscient and omnipotent via the power of Kingdom Hearts and what he would learn from the Keyblade War.
What did Xemnas go on about the entire time you fight him? "Hearts are power. Nothingness is eternal!" "Heroes from the realm of light, I will not allow it to end this way - not yet. If light and darkness are eternal, surely we nothings are the same! Eternal!" ("That doesn't mean YOU'RE eternal!")
He even reveals in DDD he wants to become all-knowing! What do you do once you amass that much knowledge?
Idk. Seems like a plan to become a god to me.
Exactly this, all this "balance-babbling" is just an excuse of Xehanort in order to camouflage and/or try to justify his hideous crimes against countless beings and hearts.
All those actually seeing something noble or "good" in Xehanort's ambitions actually fall right into the trap of his lies like Terra did for a while in BBS.
Xehanort wants to destroy the Universe by re-creating an all-destroying war and gain control of Kingdom Hearts (the true one) himself to shape a new universe as he sees fit, effectively
making him god and grant him control over all that lives.
If that's not megalomanical crazyness of a total freak I don't know what it is. He can be put at the same league as Emperor Palpatine, Voldemort, Emperor Mateus from FF II or Sauron of LoTR.
The total destruction he seeks beforehand may even border on Exdeath, Kefka or Barthandelus-territory.
So Roxas wore the twilight clothes over his organization one? Actually that does make sense because it showed an Kh 358/2days Ulimantia guide with Roxas slipping out of his black cloak and back into his regular clothes. But then what about the pants? Did he wear them over his blank pants as well? lol.
Under his black coat to be specific. Roxas wore his Twilight Town outfit under the Black Coat as those clothes are his normal street wear, including the "X"-zipper.
The coat magically alters the undergarments if you wonder about the color of Roxas' clothes and why he hasn't his high collar when wearing the coat.
Riku also wore his KH2-clothes under the black coat as did Mickey as is both seen in KH2.
When DiZ put Roxas into the virtual Twilight Town he and Riku just removed the black coat, that was all.