This case has focussed on ONE man only.
There were Three adults in that farmhouse !
Two psychotic women------------with issues ! Both on a short fuse. This,,to my mind,is the beginning of the case and should have been studied in-depth,and at length, as to the situation and atmosphere of that night. Sheila and her mother argued as soon as Sheila stepped foot inside the farmhouse.
Everything else follows,,investigations,etc.