This is beyond sick. I consider the parents enablers AND CPS would have gone right in and removed the kids from the home if this came out. Lots of cover-ups to go all the way around.
It is possible they could have boarded Josh at a place (or in a relatives family situation) that would be safer, if this continued to be a problem. With nobody that he could molest, perhaps the Lord could have worked the situation out.
Anyhow, the root problem here is sin and the thing that keeps letting sin grow in lives is a lack of grace.