I feel like many of these people are just looking for "action" to keep their own names out there for self promotion. If the Irwin's told investigators all they had knowledge of, in earlier interrogations and were treated like baby killer's I can see where they would think it's no use. Perhaps, they have nothing new to add, nothing to help. I can also understand the attorney's not wanting separate interviews. Hey, that would take twice the time of them. Yes, they could fire the legal counsel but then where would they be? They don't have the money to hire replacement.
I have seen no evidence to lead me to believe the parents had anything to do with the disappearance of baby Lisa. It looks to me like any one of a number of characters could be the guilty party.
And lastly I am of the mindset that if one beats a dog when it's down and it survives, chances are it will come back and bite them on the butt!