Instructions
Put a recently deceased Sim's urn or tombstone in another Sim's inventory. When a Sim dies, one of these two objects is always placed in another Sim's inventory, typically the Sim who is the oldest in the household.
Click on any telephone in your Sim's home. A list of options will appear.
Click "Party..." and then "Funeral Party." A window will appear with a list of guests.
Double-click the names of any Sims you would like to invite and press the check mark at the bottom right of the screen. People will then begin showing up for your recently deceased Sim's funeral.