Black family heirship situation
Please note that this post only applies to my fics, not canon. To this series specifically.
So... I've been told that my inheritance situation is convoluted. Fair, it was sort of planned like that. But I can and I will explain!
Let's start with Arcturus Black III. He's Sirius' grandfather, if you're confused. He's our first important Lord Black. He inherited the Black family from his father and originally gave lordship to his son, Orion.
Orion Black had two sons: Sirius and Regulus. As we know, by 1979 they're both out of the line of succession with one being thrown out and the other dead. So in 1979, when Orion dies, Lordship goes back to his father Arcturus.
After Arcturus' death it gets tricky. If the main line is dead, the next in line isn't from some branch of the family. It goes in the last lord's generation, horizontally from eldest to youngest. If there's no one available in the last Lord's generation, check the next gen.
So at this point you do have a Lady Black: Cassiopeia, who's supposed to be succeeded by Cygnus (the Black sisters' dad). But in 1992 they both die, in this universe Cygnus before Cassiopeia. So the inheritance stays in the generation of 1901-1920s.
In 1992 Theo's cousin Christian is technically first in line & Lord presumptive. He doesn't know tho, he's in France and lost all connections to Britain. The Burke line looks like this:
So when Christian dies in 1993 it's Theo again. Because while he is younger then Narcissa, who's next eligible in the public eye, he's from a generation older then her.
Unlike Draco, Narcissa knew they weren't getting the Blacks. She might have, if Cygnus lived a little longer, but not Draco. Malfoys are extremely exclusive, Malfoy heir is just that and nothing more, bc of the family curse (one child curse. The curse is relatively new tho, that's why Draco thinks he can grab the Blacks)
And then Dorea gets into picture. Dorea is Arcturus' cousin and Cassiopeia's sister, she is the first in line at that point. As a bonus, Arcturus actually left a will, which is a reason Harry's situation exists.
Arcturus willed everything to Dorea, bc she was his favorite child, despite being his cousin. They have 19 years age gap, he was a lot more a father to her then a cousin.
Dorea in turn willed everything to James Potter, her nephew. She didn't know she was Lady Black at that point, bc she wasn't, her will was created way back in 1940s, so to her it wasn't that big of a deal. James obviously left everything to Harry.
So in 1995 you have two heirs with truly equal claims: Theo by blood relation (eldest currently living blood relative from the eldest generation) and Harry by Arcturus' will. Thankfully, they don't hate each other and wouldn't fight over heirship, because if they did it would be so messy.
If Dorea didn't care about the boys and only cared for the Black line to be stable, she should've engaged them OR establish who's heir apparent, thus creating a new main line. She didn't do that, bc of the current plot reasons and, obviously, because Harry and Theo are gonna end up together anyway.
Please note that this entire situation is exceptional and unheard of even in universe. Usually you get internal squabbles and in-family murder cases, not this fucked up succession jumps.
(Blacks are complicated, that's what makes them interesting XD)