These constructs becomes available when you have a Level 4 Stitchyard unlocked (sanctum feature). (I hit Revered with the [faction=2462] at around this point, so not sure if this is also a prerequisite). [npc=167150] will offer you this quest Iron Solution to speak to [npc=173048]'s soul and [npc=173049]'s soul.
You then need to collect the construction components (if you don't already have them) to use at the Construct Table in the Stitchyard.
- [item=183475] drops from [npc=161105] /way 48 43 Indomitable Schmitd.
- To remove his barrier, use the [object=339646] just South of you at /way 28 43 Fuseless Special.
- For Naxx, you need [item=174076] which drops from [npc=162690] at /way 65.76 34.65 Nerissa Heartless.
[npc=159199]'s weekly quest is Bring Your Own, [npc=158298]'s is Drink to the Dead. These are a requirement for the achievement Abominable Lives.