Sirion will lash out, realize that they can't fight both Caligus and Perdan on the open field, and then retreat behind their fortifications and turtle up. The rest of ya will look for a weakness in their border defenses, but cannot find one, and eventually get bored and sue for peace.
Nivemus will probably get curb-stomped if they try to help their big brother Sirion, but I'm guessing that they are not that reckless.