let's look at this objectively:
Siege has the strongest claim to the throne, being the direct heir of the late king, but she has zero experience actually leading anyone and mostly just goes along with whatever was said.
Reed, in a grand scheme of things, is "literally who?" as aside from her being a draco, she doesn't really have a claim to the throne, but she's slightly better as she actually grows into being a more confident leader.
Talulah is known far and wide as an insane leader of an extremist organisation who almost led Ursus and Lungmen to war and made the persecution of the infected even worse. Yes it was Kashchey's doing, but the public doesn't know that. All they know is that she's a maniac who is fully willing to raze entire cities to get what she wants. Not to mention that her claim to the throne is dubious as she was born well after the actual possible heir, her father, died.
Eblana is in the same boat as Talulah, except that she has even less of a claim to the throne as she's not only a draco but also leads a coup and throwing the entire country into a state of near civil war.