Didn’t Havenport marry Miguel’s aunt? Or was Miguel’s mother a Havenport? Either way I’m pretty sure I heard there’s a marriage alliance in there somewhere.
Also I’m not sure Havenport has anything to gain by potentially destabilizing the government. It only weakens his position because he can’t call on them for aid in suppressing the rival clans.
And as you said, if his chosen side loses he will get beheaded.
If it does come fo civil war, the anti-crown factions will probably be Warburton, Wulfram, and the Salt Coast Earldoms. Cunaris and Havenport are too dependent on Aetoria’s authority.
If this is a direct result of Miguel potentially dying heirless, why can’t people just be civilized about it and hold a Cortes vote on the various claimants?