I came across @lucisevofficial analysis of Corrin's character who to put it into simple terms is an abused victim struggling with years of isolation and their half dragon nature.
In this analysis I noticed a few good points that I want to bring up with both royal sets of siblings. Heart vs Head.
To start off I do think all eight of them have been abused in the environments they grew up in. Not intentionally for some, but it's there. And I will not take slander against either sets of siblings.
Let's start with fan favorite, the Norhian siblings.
To start they did not raise Corrin, get that out of your minds right now. (In my opinion neither sets of siblings really knew Corrin, but that's for another post.) They visited an isolated child and taught them some sword play. Did they visit more when Corrin started more advanced tactics, maybe. But Corrin's main companions told through multiple supports were a disowned, orphaned, nobel, an old general whose family was killed by the king, and two other prisoners of war. All forced to serve Corrin, but they all made the best of it, some still found love and loyalty to their lord. Those were the people that Corrin grew up with.
Sorry for the mini rant, onto the siblings. They put Corrin on a pedestal and saw them as a light for Nohr. In their bloody concubine war they were already hardened, with the exception of Elise, by having different siblings try to kill them. They are extremely led by emotions, which I think is a huge attraction by some players. The Norhian siblings take the betrayal a lot more personal than their Hoshidan counter parts do. Such as shown when they use names like big sister/big brother, terms of endearment in a sarcastic voice. This I believe is due to them seeing Corrin as this figure of light that is now fighting against them. In birthright they get nasty, and in conquest, they stand by as atrocities are done. In revolutions we have them join not so much because they listened to Corrin but because of a feeling, a whim,or they saw no other choice.
Onto the Hoshido siblings, they are very much head rather than heart, and this due to their environment as well. In Hoshido it is very much duty and honor bound type of mind set. Failure and dishonor is the worse thing for these people. As seen with Hinoka becoming a soilder at 7, Ryoma's ritual suicide, and Takumi's possession. They are raised young with this mindset and it leads to a borderline toxicity that somewhat reminds me of Zuko and his obsession with honor. These kids were not physically harmed, but their mental states were definitely put through the ringer/manipulated. I think this subtler form of abuse is best shown with their relationship to Azura. They are obviously more loving, but still reserved, when she's on their side, but when she betrays them, betrays Hoshido, their home, emotions are turned off. There is no doubt in my mind they at least slightly feared Mikoto too, as shown what she's willing to do due to her own enviroment.
In relationship to Corrin at first they are somewhat stuck in the past of the child they knew, but that's kind of expected sonce Corrin was with them for like 24 hours before choosing, and in birthright they show Corrin that reserved love, as they are not as open with emotions. If you look at conquest they are much more calm when facing Corrin. In revelations they listen to Corrin before they join.
Even lookong at their retainers it's really telling. In Norh resources are scarce, you find what you can and cling to it. That's why majority if not all the Norhian retainers were found or picked up from tge streets. In Hoshido everything and everyone has a place, and a station. You learn it young and are trained to be loyal to it. Looking at even Corrin. They took Jakob in and clung to him to keep him. With Kaze he was trained young to be Corrin's retainer, and years later still holds a lotalty to the royal they were trained to serve but has never met until they spared them. Now all 8 of the siblings are friends with their retainers, you spend all your time around someone you're gonna be friends. It's just intresting how they started out, but still have similar relationships.
Like I mentioned earlier all eight of these kids went through abuse, it's practically been nonstop war for majority of their lives. How they react to the same situations, ie Corrin choosing or not choosing a side, is really telling of what they developed as "survival mode." And what I also think is intresting is what they try to project, is almost the opposite of how they really are in survival mode.