@WarrenKWoodhouse The ghost you are using could possibly be the issue. When I did the achievement I used a ghost that I had move back in with my family. The ghost was of a sim that died in game of old age and had a tombstone. I saved that ghost to the library and duplicated it.
I understand some kinds of deaths will cause issues with ghosts, like drowning.
You can try to download a ghost from the gallery that died of old age if you don't have any in your game you can ask to move in with your family. I know some ghost households spawn with Outdoor Retreat and with Discover University those ghosts appear in the households tab and are not hidden. The game also spawns ghosts for Ghost Night if you have Get Together, however I don't know if those are added to the households tab.