I'm sorry if this has been asked/answered -- I tried searching and I might have missed something.
I'm a bit confused on the strategic thinking behind the Idrian treaty with Hallandren. We are told that the treaty was written to postpone war between the factions, and once the marriage consummated, to unite the factions and presumably resolve authority claims (The Idrians have the real royal family, but Hallandren has the armies and power; the Idrians realize the Hallandren's will eventually attack once they get what they want, presumably the royal bloodline, but it at least gave them a 22 years delay).
Support for that:
In Chapter One, it says "The Hallendren needed a daughter of the royal blood to reintroduce the traditional bloodline into their monarchy. It was something the depraved and vainglorious people of the lowlands had long coveted, and only that specific clause in the treaty had saved Idris these twenty years."
Question: Why would the Hallandren priests agree to a treaty with the Idrians to marry one of the royal daughters to the God King to presumably produce a God King heir with "royal blood," when in all likelihood they would actually substitute another Returned baby as heir as part of their regular sham? Was Dedelin wrong about the motivations of the treaty on the part of the Hallandren's? And if so, why would they agree to postpone for 22 years if they got nothing in return but the off-but not guaranteed-chance that the daughter would produce a true heir?
Assuming Dedelin is not wrong about the motivations, playing this out strategically...they'd marry the Idrian daughter to the God King, she'd get pregnant (or not, but they'd claim she was), and then substitute in the Returned child, presuming she didn't actually get pregnant. But what happens when the new God King clearly doesn't have "royal blood" and can't unconsciously change the color of his hair?
Returned can change their appearance at will, but most of them don't even realize that. Whereas the Royal Family have to work hard and learn how to control their color changing hair, because it happens naturally with changing emotion. Would the idea be that the Priests would "teach" the sham God King how to change his hair color at will to allay suspicion?
I'm just not sure I see how this was supposed to play out in order to intermingle the blood lines. I know there is a way for Returned to conceive, but there was no guarantee (at the time the treaty was made) that it would happen in this case. And we know that they have a substitute Returned baby ready and waiting when they pressured for the treaty terms to be fulfilled.