What the parents should be doing is trying to put a hold on the story altogether, that is until Elizabeth is 18 and recovered from the trauma.
I think the evidence is going to come out no matter or not unless the Mitchells act as their own attorney in court.
Wanda will cut a deal for a life sentence in solitary so she won't die by the hand of other prisioners and Mitchell has said that he will act as his own attorney in the kidnapping trial.