No, Manus is still not clarified to be the owner of the Dark Soul but is indeed the father of the abyss by completely awake his dark soul fragment.
Fair point still the kingdoms existed before Vendrick established Drangelic so the timeline is still not coherent for me. Also there is no extra dialogues from nashandra about slaying the other queens and is still giving the impresion she is the only former manus fragment.
The timeline is not coherent if you think that Nashandra was the first fragment of Manus that tried to intervene with the events of the world. But we don't know that. What we know for sure is that she was the first fragment that gained a human form, and that she was also the tinniest of those fragments, and because she's the smallest and was aware of her fragility she was in the search for power. The game never states that she is the only fragment of Manus.
There is no indication she have sisters at all or being the last of getting a king, the game argument is pretty stupid when you compared the items description with the new DLC content heavily pointing you Nashandra descends from Manus in a very solid one sided dialogue in case the player dont know how to read and use his/her brain.
The game says:
The old one of the Abyss was reborn in death,
split into minuscule fragments, and spread
across the land.
The smallest of the pieces, sensing its own
fragility, yearned for what it lacked.
This, to me, is an indication that there are other fragments of Manus out there. Of course we didn't know if those fragments took human forms, but even before the DLC was released many speculated that Darklurker was also one of those fragments. The possibility of the existence of other beings like Nashandra was a thing before the DLC.
The dialogue is misleading as always because in that dialogue he refers the humans as the ones who can use the dark and fire but not as child of the dark as they were reffered in DS1 but when it reach Nashandra topic he directly says she is a children of the dark because manus. So the game heavily takes you think the manus fragments are the child of the dark and not letting you belive the other queens would be humans already using their dark soul like the darklurker, sir alonne (in some extend) and the fume knight
Well, to be fair the meaning of the dark has always been very ambiguous: Humans were not the only beings that came from the dark. The opening movie in DS says that Nito, Gwyn, the Witch of Izalith and the Furtive Pygmy came all from the dark. But the only ones that used the dark soul were humans, specifically it was the furtive pygmy who gave it to his descendants... why exactly? to put it in the terms of demon's souls, apparently that gave the humans "clarity". Then in the game we had the Abyss, and I thought that that was the place all beings came from originally (humans, demigods, etc). Then the DLC happened and we had Manus -the primeval human- whose humanity went wild and created the abyss, yet another manifestation of the dark.
And in DSII we have the Darklurker: who interestingly is a fragment of the abyss, we don't know if that means it is or it's not a fragment of Manus. Elana is also a fragment of the abyss (it's never stated that she is a fragment of Manus), we don't know much about Nadalia other than her being a child of dark that came after the Iron king had already disappeared; the only one that we know was born from Manus is Alsanna, who was born from his fears and decided to accompany the Ivory King. Many people think (including myself) that all these children of dark are fragments of Manus, Alsanna confirms that there are others like her, and the pattern: a child of dark that search for a powerful king repeats itself 4 times so it may be possible that the queens are sisters that share the same objective. Since we don't know when they came to be and what they've done since they were born, Elana, Nadalia and Alsanna going to different lands before Nashandra met Vendrick is not exactly a contradiction in my opinion.
I actually like what they did with the story in the DLC. They finally gave us a "happy" ending.