You've got me interested. Please go on.
I have wondered if the R's were entirely truthful in reporting they did NOT feed JB pineapple. JB went to the kitchen to help herself to some pineapple (PR and JR were truthful in reporting they did not know about this) and maybe waiting for a secret visit from Santa Claus
Perhaps the R's heard sounds in a kitchen, sounds that sounded like a burglar, thought JB was an intruder, so they wacked her accidentally
they heard sounds in the kitchen, they thought JB and BR were in the bedroom asleep, they went downstairs with a baseball bat, and they swung in the dark thinking it might be a burglar and it turned out they accidentally hit JB. They heard a cracking sound, and realized they fractured her skull. Possibly BR went downstairs and struck JB
-- perhaps JB was in the kitchen and heard her parents coming downstairs and so she ran off and hid, and the R's believed there was an intruder so they set off in the house looking for a burglar when they struck at JB. Maybe she knew she wasn't supposed to eat pineapple or that she violated her parent's curfew.
They made a decision to stage the crime scene rather than call 911, as they realized the strike was mortal. They then stage the crime scene.
Mistaken a family member for a burglar and then striking them has happened before. One possible variation of this idea is that PR or JR were having a visit from a secret lover, and PR or JR caught the other in adultery, swung at the adulterer and accidentally killed JB as an innocent bystander, or struck JB to prevent her from reporting to the other about the adulterous affair. The DNA obvious came from PR's bf (or JR's bf). This secret bf helped with the staging and obviously carted off some items w/him. He may have written the RN (consistent w/forensic linguistics) etc. Under this scenario, PR + BF might have done everything without JR or BR knowing anything. PR dictacted the RN entirely to him.