I think it will be helpful to explore materials in this order:
This article from the Leader-Telegram April 19, 2015. So far as I know, this is the first public report of what is happening at Valleybrook done by an independent source. Various people from the church have been public, but always offering their own viewpoint - the LT article is the first I know of to attempt an unbiased overview, for whatever value the word "unbiased" has for anyone.
A church member (or members) have a blog, "Tales from the Cult". Before reading the blog, go to this post which has the original sermon about "Knitting".
The above article ran with this story, an interview with Judy and Bob Hagedorn, parents of Nate, and then there is a video that the parents made talking about their son
My comment: the idea of "knitting" as offered in that sermon, and as lived out, is to me really outlandish. I see nothing biblical in it, other than the loose connection to the story of Jonathon and David. This is bad scriptural interpretation, IMO. Really bad. Horribly, terribly, no good bad. Wow.
Updated April 20, 2015: to add the secondary article, the interview with the parents.
Updated Dec. 7, 2015: another article in the Leader-Telegram about how the new leadership is taking steps to right wrongs found in pastoral abuse scandal, followed by new revelations of alleged fiscal mismanagement.
As I come across more things, I will keep adding them here.