Aurora's My Grandson, Myself ploy will raise some eyebrows. Being royalty, some sort of witness would be expected to ensure the infant was indeed born to the queen, which doesn't give her much room to pose as her own child. Even a workaround such as being in cahoots with the witness would be difficult to pull off, given that the rest of the Starlings die at age twenty-five.
The official reason Grim gives for wiping Isla's memories of their romance so that she could seduce Oro is because he and Aurora believed Isla wouldn't go along with it if she was still in love with Grim (without discussing it with her first, mind you). However, Grim wiping Isla's memory makes sense for another reason; due to Oro's flair making him a Living Lie Detector, it's very likely he'd be able to tell if Isla had ulterior motives for trying to seduce him and/or that it was truly Grim she loved (though the book never brings this up).
The curse of Starling, which results in everyone dying by 25, has some horrible implications for their society that aren't really discussed in-depth within the book. Namely, that everyone would have to start having children veryyoung (and would probably be encouraged to do so to maintain the population), all the children would be orphaned before or shortly after they reach their teens (depending on just how old their parents were; if you do the math it gets particularly Squick-inducing) and would end up having to fend for themselves or be raised by people not much older than them, and people would likely spend most of their short lives focused on trying to reproduce and ensure their children are looked after once they're dead, with childhood being incredibly brief. Then there's the fact the human brain usually doesn't finish developing until your mid-20s, in particular the prefrontal cortex, the part of the brain responsible for rational/logical decision-making, long-term planning and impulse control, all of which are vital to successfully running a society. Overall, being a Starling seems like a bleak and dysfunctional existence, likely resulting in a population with a lot of mental and physical health problems.
One of the rules of the Centennial is that no ruler can have an heir, so that if a ruler dies their line fully comes to an end as specificed by the prophecy (which is believed to be necessary to break the curses). Most of the realms appear to be governed by hereditary monarchies, with a ruler's title and powers being passed to their nearest blood relative if they die (e.g. Isla became the Wildling ruler after her mother, the previous ruler, died, while Oro's older brother was King of Sunling and had no children, with Oro getting the position upon his brother's death). The fact that not a single one of the rulers - even the ones who have been around for centuries - currently have a child or sibling who could be their heir by the events of Lightlark seems like a huge Contrived Coincidence. It indicates that most of them would either have to be really careful about contraception or else practice celibacy if they're exclusively attracted to the opposite sexnote Azul is gay so he wouldn't have to worry about accidentally knocking up a partner, while Cleo is bisexual and so could theoretically limit herself to female partners... or resort to other,darker methods to ensure they're heirless.
The book doesn't explore in much depth how Wildlings have been shaped by their curse, though it can get pretty grim if you think about it.
The Wildling curse compels all Wildlings to murder a personthey fall in love with, so the entire population would have to take steps to avoid this. All sexual encounters would have to be purely physical and lust-based with no deeper feelings involved, or done solely for the purposes of reproduction without any attraction at all; while apparently sexual liberation is a big part of Wildling culture and some people have no problems with casual sex, other people would probably find this arrangement unsatisfying or downright depressing. Wildlings likely can't spend too much time with a person they're attracted to because of the risks of developing deeper feelings; it wouldn't be surprising if the Wildlings had some kind of law against this, if not outright demonising it. Heck, considering some romantic relationships start out as friendships, Wildlings would have to be wary of their friends too. The end result is a society where people actively avoid forming close bonds and cut short most of their relationships, just in case one or both of them catch romantic feelings and turn homicidal.
The curse doesn't specify that the love must be mutual, so there may be cases of people getting murdered by someone they thought of as a friend or were merely acquainted with. It could also result in people taking their own lives or resorting to other drastic measures to prevent themselves from harming someone they love (unless the curse prevents them from doing so), people killing in self-defence, people killing each other, and potentially family and friends getting hurt/killed or taking matters into their own hands in order to protect loved ones targeted by the curse. And then there's the emotional/mental fall-out for Wildlings who were either forced to kill a person they loved, or were forced to kill someone to defend themselves (especially as they likely knew and had some kind of bond with that person).
The incident with Isla's mother implies that with enough willpower a Wildling could resist the urge to kill their love interest, though this still doesn't exactly solve the issue because a romantic relationship where you know one or both of you might snap one day doesn't sound especially viable in the long-term.
It's not specified how the homicidal compulsion works. Is there a proximity factor, so if a Wildling stayed far away from their love interest and never laid eyes on them, would that succeed in repelling the curse? Or does the curse essentially turn Wildlings who fall in love into the Terminator, compelled to hunt down and kill their love interest above everything else?
The fact that Wildlings must sustain themselves by eating human hearts brings in a lot of logistical concerns. How are they getting enough hearts to sustain their population? There's mentions of them killing thieves who encroached on their territory, but surely there aren't enough people that are Too Dumb to Live. Has this need ever brought them into conflict with the other groups? Have Wildlings turned on each other to fulfill their need, causing their own population to dwindle? One particularly horrifying theory is that Wildlings raise humans like cattle.
