Find NPC tombstones

Hey guys,

Is there any way I can find the tombstones for NPCs that have died? My sims has a lot of relationships that at this point.... is more ghosts than live sims.

Is there any easy way I can get rid of them? I know some of them have tombstones, but others happen to be townies.

Also, do spirits fade away automatically, or is removing them the only way to get rid of them?

Thanks!