Sometimes I wonder how authors view small children. Sure they can act stupid at times, but feels like these ones should both know how stupid it is to act outside the guardians knowledge, and have already been warned not to if possible. Particularly when they are taking measures like setting up barriers as they know they are currently targeted.
Also, how did they leave that note, with the gigantic barrier in place?
If they take the kids as hostage, the simplest way to solve it would be to take the lord et al as hostage in return, before showing up at the fort with them, right? Feels like any other method would endanger the twins, as simply showing up should have at least one of them executed instantly (if they aren't already). Both to show the threat is serious, and because it is simpler to only hold one hostage (although with a platoon at their use, I guess it is possible to hold them separately, so even if they can save one the other is a backup).