Hello! What would your Abdullah's dynamic with his siblings be?
So, first things first? You are a joy and a delight, thank you ❤️
I often joke a little that, despite being virtually the middle child in a lot of ways (unless I get silly with things) Abdullah still radiates chronic older brother energy.
The only one exempt from this is Mehmed, who, while everyone else might idolize Mustafa, is the one Abdullah looks up to. In Abdullah's opinion, this is the brother the most worthy of the throne, able to keep them all safe, and so, initially, any support he garners is conditional on it being to provide further backing to Mehmed. He values his older brother's heart the most and wants to be the one handling the shadier things to let it continue to shine (him and Ilyas should talk).
It's also why he's crushed when Mehmed dies (and takes the swearing of vengeance after realizing his death wasn't an accident very personally indeed).
Him and Mihrimah are a bit more of a dark horse for me? I fear I've focused too much on the brothers and not enough here. If she still supports Bayezid, excusing away a lot of his problem areas, then there's going to be some friction between them, but her having another brother throne into the mix altogether could change things.
Back when Abdullah was ill, Selim stumbled across his door very much by accident, trying to get away after a fight with Baeyzid. He wasn't meant to be there, given the quarantine, but Abdullah hears someone trying to leave and begs from the other side of the door, desperately for them to stay. And so...Selim stays, telling Abudllah anything and everything from the other side of the door until he's dragged away.
Afterwards, Abdullah seems to have a particular fondness for Selim as the only sibling that came to visit him and it curdles in Selim since it feels unearned. Particularly when Bayezid calls out, eventually, how Selim is just using Abdullah to make himself feel better (aka: have someone to support him sometimes) but Abdullah just shrugs and says basically, "Yeah, so?"
Abdullah loves Selim, faults and all, and it means a great deal to his big brother.
Bayezid is...ah, Bayezid. It's not that Abdullah doesn't love his younger brother because he does, but it's a matter of where, while all their other siblings are, in the scheme of things, easy to track in their problems, Bayezid is not. Bayezid, in fact, decides to invent new, entirely insane ways to bring Abdullah migraines and then persist in not allowing his brother to help him clean things up because he either doesn't think he's done anything wrong or believes all will be forgiven anyway. Often both.
There's, unfortunately, a bunch of little things that start to strain their relationship, such as Bayezid's support of Mustafa and his inability to understand why Abdullah has to hold Mahidevran accountable for Mehmed's death, possibly Huricihan's initial crush on Abdullah instead, or Bayezid's constant antagonisms and refusals to behave and be at peace (he does not respond well to Bayezid, after Selim attempts to offer a truce, claiming that Selim should be dead).
But still, despite knowing that Bayezid wouldn't be able to accept the same out he'd give Selim (basically, this is my show and if I say an Ottoman prince could fake the death of his brother and that brother's family to let them live in peace then so be it), he's crushed at Bayezid's end and how, even then, Bayezid won't accept any offers of salvation from his corner.
Cihangir is...complicated. He's the babiest of Abdullah's brothers, the one whose medicinal treatments Abdullah learned to craft so there could be less hands directly involved that could introduce something harmful. But Abdullah's presence is often corrosive to Cihangir in a way he can't quite understand.
It all comes down to how, after surviving smallpox through the aid of a miracle, the entire family is very precious about Abdullah's health, fussing over the slightest cough. And, based on the attitudes around gender norms of the time, Abdullah can't be perceived as precious in health and coddled. So he learns to treat his own illnesses, shaking off any smothering. It makes him like Cihangir but not really since he's able to still fulfill the traditional role of an Ottoman prince, so being around Abdullah sometimes just reminds Cihangir of why he's different and even more so when Abdullah insists on shielding him from the coddling and trying to encourage him.
(Cihangir's death, like Mehmed's, destroys him—he hates the idea that it's the two brothers he finds the most innocent that are taken and he couldn't save them.)
I think, for a good chunk of it, Abdullah is just kind of to Mustafa what Cihangir is to him. It's not that Mustafa (or even Mahidevran initially) are cruel to him, but he's never able to forget how Gülşah once sounded so delighted to be informed that he was unlikely to escape the sickbed, back when the throes of smallpox left everyone convinced he couldn't overhear or, at least, comprehend them. It makes him consider everything with a far more critical eye and he knows that, deep down, even his own family (his aunts and grandmother and Ibrahim) don't love himself or his siblings like they do Mustafa. And so it kind of paints Mustafa little in a guilty by association type of way where he can just never fully trust in the love that's being offered.
It hurts Mustafa, of course, because his oldest brother genuinely is overjoyed that his half-brother didn't die, but then said half-brother...distances himself from him?
While everyone else (except perhaps Selim?) looks up to Mustafa, Abdullah looks up to Mehmed and goes to him first instead and...yeah, it hurts, and, yeah, Mustafa is almost sometimes jealous.
Then comes the shock of Mahidevran being behind Mehmed's death and Abdullah's "test" to Mustafa in regards to it (I can expand on this just here given how long this already is) and the well's kind of forever poisoned.
It's interesting, though, to try thinking through the mindset of the Mustafa of the show since it's so less straight forward than the historical version? Like, he winds up thinking, "Okay, so I'll have to kill a brother...but it's his fault for opening that path to me!"
And...like...buddy, low key, sure, but...wtf?
(Bayezid and Cihangir definitely accuse Abdullah of "causing" Mustafa's death and, after not being able to prove a direct hand from him in it because...there's not one...they instead point to how Abdullah "murdered" Mahidevran, which...is a whole other can of worms, but I can see how they think this is what "changed" Mustafa and they don't want to confront the gray.)
