Trivia: Early in the film, an SUV is smashed by a wrecking ball in front of Whipstaff. A real SUV was smashed for that film and it was obviously one that had been in a wreck previously. Notice that the passenger door is crooked and pulled away from the frame.
Trivia: The interior of Whipstaff was built at Universal Studios. Early in production there were several moderate earthquakes in the Los Angeles area and many of the large cracks that appear on the walls, etc. were real.
Trivia: When Karrigan and Dibbs are trying to get the ghosts out of the manor, they contact 'The GhostBusters'. Dan Aykroyd reprieved his role as Dr. Ray Stantz and fled from the building suggesting that they call someone else.
Answer: The Ghostly Trio were, at the time, playfully teasing James, so Fatso wearing something else instead of what Amelia was seen wearing in the photo, was just a way for them to have some fun at James' expense. At the end of the movie however, they did keep their promise and let James have one final chance to speak to his wife.
Why that specific outfit, though?
Again, to playfully tease James.