Twice they interrupted Jack before he was about to kill Wendy. First was when they wanted him to kill Dick and then after to get Danny. Yet if they just shut the hell up, Jack would have finished off Wendy anyways and dealt with both Dick and Danny.
share1) Dick and Danny had the shining. The more time Dick was around, the more time he and Danny could come up with a plan to stop Jack. It would have been 2 people transferring mind messages to each other and they would have easily been able to take Jack out most likely.
2) Jack was the one who was obsessed with keeping the hotel up to code. The ghosts too probably realized that dumping the boiler was more important than indulging in "correcting" Danny first.