Fire NPC, or Cast out Son or Daughter is how you remove an NPC from your household. The NPC in question has your Org ID removed from their record and they become just another unemployed NPC. If you cast out a family member, they cease to be family and can be hired just like any other NPC. While it was rare, "unfaithful servants," or "unfaithful children" were "cast out."

Wives are another matter, you have to petition the pope for a divorce or arrange for your dearly beloved to meet with some fatal misadventure, rather than merely casting them out.