What could Derrick possibly say that would be a revelation? Josh abused his sisters and a friend, and wasn't held responsible, nor did he make restitution. He's a scumbag, into porn & hookers.
All this & more is public knowledge already.
The Duggar adults make shady business deals, probably cheat the IRS and have made a family career of lying, grifting and neglecting their children. They are uneducated, sleazy and lazy. Jim Bob & Michelle have manipulated and brainwashed all of their children, for all of their lives.
Most importantly, what could Derick prove that would be worth publishing?
And I just don't think he has the balls.