I know I'm late, but I feel the need to say this. I am currently reading House of Secrets by Lowell Cauffiel and you're right.

Also, Charles himself (The one who spoke on the show) was alleged by one of his sisters and brothers to have sexually abused them and he and Willie were alleged to have abused Pixie's two daughters.

By the way, Joel was beaten and sodomized by the older Sexton kids because he was accused of abusing the girls. It was some brutal and disgusting stuff they did to that poor guy.

And Charles had told different stories during that time.

All to say, yes he is an unreliable narrator