How do I do whatever it is I need to do to them in order to make one of those mystery weapons someone mentioned ?
Or do I need some special blueprints from Sector B etc first ?

Here is a walkthrough of how to get the guns:

https://www.youtube.com/watch?v=eyxhSO5Xpf8

Thanks. They look like nice guns. Did you ever find out if the brother appears BEFORE triggering the mission ? Your voice is very relaxing.

But what is SOLIBOR'S SWORD ?? I tried Googling for it, and there's a German Youtube, but I don't speak German and I don't have the patience to sit through 27minutes of German language just on the off chance that I can work out how to get/make Solibor's sword.

He does appear before however you need to pay 3 screws instead of 1 if you do it that way. If you do the quest from the start (giving brother his food) than you only have to pay 1 screw when creating the weapons.

You can get the sword from the Kings hidden tomb or at the traders (rare), you can't make it.