How COULD JB back it up? By George admitting it and then getting arrested himself for incest and child molestation?
And Lee the same?
I don't know if Casey is being honest or not...I just know as a sexual abuse survivor myself I was alot older than her before I was able enough to get over the shame and speak out about my own abuse.
He could try to back it up by some expert examination of KC. Some detective work about the past of the family, for example KC's childhood friends, school, ...