After you install Ambitions, the ghosts will not only not stay in the graveyard, but also take a ride to someone's house and go do their work as prey to Ghost Hunters. I had figured that out once I tried to divorce Steven (guy on my sig, my main Sim) and his Ghost Wife, to whom I had built a memorial on the graveyard.
The only solution I could think of is "go play ghost hunter, find your haunting wife, divorce and sell her to the facility (or make her a painting in the wall, like in Luigi's Mansion)". I will be testing that soon.