These rebellions in stories always baffle me, they decided to kill/betray the strongest people in the Tribe, dividing it and making it into civil war, which will make the tribe weak and easy to conquer by other tribes especially since they are only at ceasefire with another tribe for the moment. Not to mention they want to imprison Grace who is the daughter of the Glow of the other tribe meaning they would have at least two tribes against them while they are extremely weakened.
I'm not good at politics nor war so i might be very wrong, but i still see this as suicide on their part and nothing more.