I made an alien just to call down a meteor onto Oscar's parents in the Oscar's Childhood video. I'm still wondering what to do with their ghosts. They are safely waiting in their world for me to make up my mind as Oscar h as been transported to the boarding school in Chocolate Cake Island.
I see there are three things that could work with this scenario @IreneSwift has just had.
1. Continue on playing and accept you have 2 new ghosts in town.
2. Go back to an earlier save and forfeit the money
3. Pick up the tombstones and take them home and get a Philosopher's Stone and bind the ghosts so you have control of them and get them to eat Ambrosia
I've done each of these things at different times in different games. They all work. It's just what will fit with the story.
Have fun and force it to work for you.