Now I remember, after you defeat them they're in "Death" state. You cannot tame "Death" NPC but if you go inside to any cave and carry their corpse, if you check again, the "Death" status is gone and after that they can be put into Iron Fence.
I just vaguely remember when their debut in this game you don't need to bring their corpse into any cave, just put them into the cage and their favorite food is the same or similar with Native Male and Female
For Death Wand, if it not available to any bench, trader, old man or older brother, it is not craftable