You have two options.
The easier method would be to use
The Urnstone Spawner .
A more tedious method, and the one I use, would require the
SimBlender and the
FFS Lot Debugger.
1. Go into
Miscellaneous/
Miscellaneous and place the
SimBlender and
FFS Lot Debugger on your sim's lot.
2. Pause your game and click on the
SimBlender. Go into
Transport and select
Enable Summon Menu.
3. Go into
Transport again and click
Summon. You should see a bunch of family names. Since the sim you'd want to summon is dead, go into the
Default family as that's where deceased sims are stored.
4. Find the name of your sim (they'd have their full name listed) and click on them to summon them.
5. Open the cheat console (CTRL+SHIFT+C) and type
boolprop testingcheatsenabled true into it.
6. CTRL click on the summoned sim and select
Make Selectable. They should appear in the Sim Chooser. Click on them.
7. Using the summoned sim, hold CTRL and click on the
FFS Lot Debugger. There should be an option called
Recover Tombstone, or something like that. Click it and once you unpause the game, the sim should fade leaving their tombstone behind.
This is provided they have data though, since I seem to remember the Goth ancestors being unlinked, but I could be getting confused. The first method would be more ideal and easier.
When a game is predictable, it's boring.
That goes for any medium that isn't life.
That's why The Sims 2 is my favourite sims game.
It has elements of unpredictability and everything feels more involved.
The Sims 4 is another story altogether...