How do you get him off the Roller coaster [just put this on the blog so I can read it.]

To get him off the Roller Coaster, you must ride it. He should get off after that.

Once you have re-united the ghost kid and his mom, the ghost kid will never be on the roller coaster again. To unite them:

You must learn the Ham-Chat word "perksie" from the 4th floor of Boo Manor and go in the elevator to go back downstairs (DO NOT use the mirror, you will be brought all the way back to the 1st floor). Go in the room with the oil painting of the crying hamster (the ghost kid's mom) and "lookie" at the oil painting. There will be a sniffing sound. Use "perksie" and the crying hamster will come out of the painting as a ghost. She will say that her son has gone and has never come back. He will be at Fun Land. The rest is for you to figure out (There are other threads about this to look at if you need help).