I am pretty certain Ayua is William and Miru's daughter, I don't think there's any hidden twist, there are plenty of plot twists to cover already. As much as I like theories, we're basing them all off the characters we've seen, and there will be more characters. We will see Elena Petrova at some point (in both games) and we will likely see Donna in SG. Most likely way down the track there will be some interaction with Sonya's parents/brother, and Nia's family will appear. We'll likely see NIka confront Mila's abuser. There's all the basketball teams from the other universities, there's Elsa's circle of people, Bella's racing circle. Melanie has yet to be seen in the presnt day. There will be a lot of characters that will be connected by circumstance rather than related.
Vanessa being William's daughter with Vanessa and Nick believing Vanessa is his daughter is super chad-level fuckery. Entirely possible. But given heterochromia isn't always genetic, Ocean can be throwing in an obvious red herring. Vanessa and Zara's mom can be someone entirely different we haven't seen. Could even have been someone at the bookclub. Leia is a likely choice from the people we know, but there's nothing saying that connection is there. But getting back to patreon issues - if Vanessa is Leia's daughter, Nika can't be related to William. Ocean's not dumb. For NIka to be related to William, the the same situation. Given Ayua keeps wanting Nika's dick pics, and is starting to show more sexy poses - if there is any lewd with Ayua, we basically have confirmation of who Nika's dad ISN'T (In which case William can be the father of all Wollust without any problems). Ocean's not going to play with fire when he was cautious to the point of censored dildos from Season 1 to bring the lewd content down to try for 16+.