Young's husband Jason has never been charged with Michelle's murder and has always maintained his innocence, but a judge in a civil suit filed by the Fishers found that he "willfully and unlawfully" killed her.
The new lawsuit filed on Wednesday also asks for a psychological evaluation of Jason Young.
Among other things, the new lawsuit charges that Jason Young "brutally murdered Michelle Young at their residence," and says "the plaintiffs, jointly and individually, are fit and proper persons to have the care, custody and control of Cassidy."
It goes on to say that relations between the Fishers and the Young family are not good. It claims that Jason Young has not allowed phone calls or many visits between Cassidy and the Fishers. It also says gifts sent to Cassidy have been returned.
The lawsuit says "prior to Michelle's murder, the defendant engaged in a pattern of conduct that was degrading to Michelle, erratic and inappropriate." It accuses him of extramarital affairs, and says he even allowed one woman he was sleeping with to live in his home with Michelle in the month prior to the murder.
In another part of the lawsuit, it claims Jason Young got drunk at a friend's house and was taken to the bathroom. It alleges he came out of the bathroom naked and sat on a couch.
It says, in recent months, Jason Young has attempted to solicit dates online, and has even posted pictures of Cassidy as part of his dating efforts.