Of course, they were free to chose as they willed. Highmarch viewed them as brothers, not vassals.
It remains a poor decision on all accounts, in my books, about the worst they could have made.
Highmarch turned on Perdan, and Perdan only. Vix's decision to stand by Perdan was much more grounded than Fallangard's decision to do the same. Highmarch's new position made Vix vulnerable, but did no such thing to Fallangard. The only way Fallangard could come out losing from Highmarch' flip is by going after Highmarch themselves. They really shot themselves in the foot. They could have went to attack Caligus, draw forces away from Vix and Highmarch, instead of joining in with Vix and looting Winkamus.
And it's not like they'll gain anything from this. They picked the losing side, and put themselves in an extremely vulnerable position doing so.
But anyone that goes against you makes their decisions bad.
