So, as I was saying, today I'm elaborating on it.
Red, much like Ella, grew up in an abusive household that she had to basically survive in. This can be seen in how Red already knew what had to be done the moment Chloe broke the vase. Red immediately knew to act because she also grew up with an abusive mother figure who would punish her harshly when catching her in the act of doing something that would upset her.
Both Red and Ella were disillusioned with the reality of the privileged aristocracy of heroes (like how Red constantly mocks Chloe for being a privileged little princess and how Ella literally calls Bridget the only exception to the idea that all princes and princesses are bad news) and how oblivious they are to how life works.
Both Red and Ella's lives, however, turn on their heads the moment they get to know Charming better (Red's life changes forever when she and Chloe time travel together to the past; Ella's life changes forever when she dances with Charming at Castlecoming, which leads to her own fairy tale) despite not exactly vibing with them the first time they meet.
Both Red and Ella had to transition from a very hopeless and toxic environment to a life full of riches, privileges, and support they couldn't dream of, along with the pressure of being a perfect princess. We know that in the original fairy tale, after Cinderella is identified thanks to her glass slipper, she gets to marry Charming and live happily ever after with him, but how does this translate to the Descendants AU version of her? Not too differently as I could imagine that Charming would use his status as someone who has to pick a consort for him to marry in the future, and since he both likes Ella and most likel learns how she lives and decides to pull her out from that environment, meaning that the next night after Castlecoming Ella would be sleeping in a royal bed in her very own chamber in the castle and then be woken up and expected to be the prime wife material for a prince (not too unsimilar to how Red woke up in her new bedroom to the idea that she's supposed to be a pretty princess that acts accordingly, along with how Ella put immense pressure on Chloe herself). I could imagine that the girl who was all about "royals suck" would feel so out of place when she's suddenly given all of this pressure and the privileges royals possess on a daily basis. Also mirroring Mal's story in Descendants 2.
And of course, let's not forget about the romantic stories of both Ella and Red. The idea behind both of their romances is that they get to experience a new kind of love they didn't think they'd ever get. Red gets to have a romance with someone who doesn't judge her, someone who doesn't expect her to be anything but herself, someone who doesn't push her to be something she doesn't know she can be. In the same vein, you have Charming, who loves and is devoted to Ella unconditionally, someone who doesn't want to take advantage of her and instead wants to make her happy and help her out, someone who also offers her a way out. They both also have a dance during the dead of the night that feels beyond magical for both of them... they also both get left behind because of the plot and for the sake of female "best friend" priorities, despite the boys being their "heroes in shining armor".
You have Red and Ella having to bridge the gap between their former and current selves.
And then we have Bridget and Chloe, both too good for the world they're living in. Both too kind, too moral, too naive, and privileged to comprehend that life doesn't work how they expect it to work. You have the homeschooled Bridget who doesn't know how to make friends and thinks that giving people cupcakes will build meaningful relationships. And you have Chloe, who immediately compares a mean person to their dictator parent, working on a very black-and-white morality with no room for nuance.
You have both of them essentially getting to step out of their bubble thanks to their less fortunate VK BFF, who helps them give support and a reality check regarding their views.
You have both Bridget and Chloe be aware of the romances their BFF have with the pretty boy they like (Bridget knew Ella and Charming liked each other before the ball, Bridget "I saw through her", and you have Chloe cackle at Red being so caught off-guard by catching feelings for Luis after his "first free rescue").
You have both Bridget and Chloe believing in the good in others, with how Bridget didn't want to give up on friendship with Uliana and how Chloe didn't want to completely give up seeing Red as a good person and getting hurt whenever Red would not conform to her perception of reality, and having her go back and forth on whether or not Red is really evil.
You have both Bridget and Chloe eventually learning the nuance, but still failing to properly balance it off, as you have Bridget, who clearly learned that forgiveness is not for everyone, to the point that she threw a mentally ill man to the prison island and only let him come back out of kind formality and not because she wanted to, and then you have Chloe who adapated more rebellious and amoral methods but ending up being a bit self-centered with their stance (kind of what led to her villainy).
You have Bridget and Chloe not willing to entertain a Hatter communicating with them (like how Chloe doesn't listen to Max when he tries to comfort her after the chess game, despite him being right and coming from good intentions; Bridget not willing to listen to Maddox trying to prove the pocket watch's existence).
You have Bridget and Chloe becoming corrupted after a VK tricks them and becomes a villain with straightened hair over it. Uliana pranks Bridget, which leads to Bridget eventually discarding all morality in favor of being a dictator, though it's unknown if the curse the prank induced influences Bridget or if the humiliation alone drove her over the edge. And Chloe puts on a bracelet Max made for her that gets rid of her morality and inhibitions. You have them essentially transform into the worst versions of themselves that are cold, homicidal, disloyal, dishonest, and calculating.
You have important part of motivation between Bridget and Chloe turning evil feeling betrayed and discarded by their best friend (Bridget was heartbroken over Ella not being there for her because she was off with her prince; Chloe got upset over Red developing new bonds with everyone while actively ignoring her input like how she befriends Max and has a beautiful night with Luis, while Chloe ends up crying alone over her best friend making her a bait to a murderous flower).
You have both Chloe and Bridget obsessed with the idea of the future where they're in charge and where they don't need anyone to rule (Bridget wanting to rule a million years with fear while executing Cinderella; Chloe wanting to time travel to a period where she's the supreme leader that discarded Max and Red).
You have the lesbian counterpart to their bisexual best friend (as Bridget and Chloe are both highly lesbian-coded while Red and Ella are bisexual-coded).
You have both Chloe and Bridget bridge the gap between their evil and good selves.
You have both couples going through both break-up and make-up sequences (though Bridget and Ella are comparatively way more meta, while Red and Chloe are straightforward).
