Lots of heat and NO impact guns. Out of the hundreds of axle's ive taken apart I probally only broke a half dozen or so bolts.
I would not call your knuckle's unuseable, I mean the bolts can be drilled out or welded out and the lower caps just need heat to pop them out.
Run a Tap to clean up the trheads and they will be fine. I would not consider them done till there crakced, even then plated knuckles will last for years if done right.
Jason.
I was able to remove the knuckle but the lower cap ended up damaging it to the point that i want to replace it for safety.