so all three of them are the heirs, the document about succession, plus the accord state that the three of them effectively rule jointly with slightly different roles, and that whoever's the youngest (Ludir I think) will be the 'king' and take someone as his bride that isn't mentioned. Unless I'm wrong?
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Possible Spoilers
Ludir would seem like the direct heir, but the rules of succession require him to be married at the time of his father’s death.
Assuming Lysna and Eirlov are dead (Actually I’m not even sure if that matters) then I think Lonara becomes Cynai-Taalei, Temig becomes Beelon, and Ludir would be Calserom to their kids, with tradition stating that Ludir will provide the beelen to the first heir.