I always took the William is everybody father more as a community meme than a real possibility. If we think the knows LIs of WiaB, and even lewdable ones there is only Ayua and her sisters, Sasha and the Rivera of the first team, maybe Aziz - and those ones may be way to old for that-. everybody else is just pure speculation, including Nika and Nami. The NTR elements of WiaB also offers a complication as some of those might not be William's, who is to say that the antagonist was not bang the other half of Wollust ? Leia can't be canonize - maybe not even a LI anymore- Katie we don't know much yet, Helen can get pregnant ? Dana, Gina, Monica, the bartender, Zoey to yet be mentioned. Of the knows LIs for Nika, only Nami and Sasha are a problem the rest don't seems related in any way with William.
Regarding the closeness of the heirs, that depends on how are the family relationships. We know that at least Katie is going against the coaches of the first team, that are backed by somebody else, so I don't think that the 3 families are as friendly as we might think. Maybe the Zanes and Petrova are but not the Revera's ?
Is a interesting idea, that makes perfect sense. The bit about the book club is why Charlie is so serious about it, is the only reason bored middle aged woman ? Is good enough reason, but the way that we can stir shit seems suggest a more complex issue, bookclub seems divided in those who suport charlie and those who not, is spicy novel the only reason ? If those family is as close as we think they are and ZPR is now not as united as once may have been, the split between the families may be splinting their common spaces. Katie plotting against Genevieve, people wanting to overthrow Charlie. It may seems like a stretch, and it is, but before a cism people will divided themselves. I don't think that much that we do will remain a secret, that is why I think Nami route will be a wild ride, Ocean just needs a reason as why is so wrong for them stay together.
Curious idea. But Bella is not one of the big families, why would she have information about Nika ?