I still like my theory. I think PR caused the chronic damage to JB's body with corporel cleaning (which imo is sexual abuse). I think PR accidently killed her that night, probably due to rage over bed wetting. And I think she convinced JR that BR did it while molesting his sister, enlisting his help to cover the crime by staging within staging (She staged first before JR was aware of JB's death, then he helped her stage, believing he was covering for his son). I think JR at some point figured out he isn't sure which of his loved ones killed his daughter, but was now complicit and had to hold firm to the story.