You cannot "kill" ghosts in The Sims 3 (Wii). They are immortal NPCs. However, you can make them leave permanently.
testingcheatsenabled true → shift-click ghost → "Trigger Age Transition" (PC method).PC Version Note: If you have PC Sims 3, use testingcheatsenabled true → shift-click ghost → "Trigger Age Transition" → "Pass On" for clean removal.