Have weak casus belli
[] Attack Thunder Speakers to stop border raids (Declares war with goal of stopping attacks, Highlanders will join, likely brings in Thunder Horse and Xohyssiri)
Exploits our current good stats to punish raids viciously. Helps cement the alliance with Highlanders, but this would also have a risk of either cementing their new allegiance or cause an early breakup.
Note that the Thunder Speakers and Xohyssiri JUST got their asses kicked recently, their armies are not in the best condition. But the Thunder Horse are too far to fight proper, which adds a chaos factor.
[] Send an envoy to request the Thunder Speakers rein in youths (-2 Diplomacy, chance of TS king actually complying, small chance of triggering war)
Ensures that Magwyna's legacy is a golden age if it succeeds. Remember, Heroic Diplomat here. She has a decent chance and worst case nothing happens.
[] Ignore the issue (-1 Prestige, large chance of loss of stability)
Yeah no, most of the disadvantages and none of the advantages.
Question of succession
[] Support son (-1 Legitimacy, heir becomes Yehlmyn [Mediocre Martial, Good Diplomacy, Heroic Admin])
Hurts our system to ensure we got a Hero Admin leader.
Noting that there is a non zero chance of war and he's not much of a warrior.
This is exactly the sort of example we don't want to set for subordinate chiefs. Remember Chariotman?
[] Remain quiet (Next king is probably standard)
Noting that he still has a chance of winning the title on his own and even if he fails at his bid for leadership, he'd probably still be the clerk chief.
Sets a powerful example of rising by your own merits. Might finish the realization Attrikwyn is currently arriving at.
For now:
[X] Send an envoy to request the Thunder Speakers rein in youths (-2 Diplomacy, chance of TS king actually complying, small chance of triggering war)
[X] Remain quiet (Next king is probably standard)