Circumstantial proves nothing,,and I'm no expert. A person can be all sorts of things,,but a murderer is stretching it a bit without any evidence at all.
Yes,,Sheila was shot-------the first time,,whether intentional or not, we'll never know,,but I think June delivered that one,,and it's quite possible that it was the second time too as it didn't happen long after that first shot. Both women were in the bedroom at the time,,both sitting,,with the door propping June up because there was blood where she'd leaned against.
Sheila would have slid from a sitting position to where and how she was found.
The rifle would have been on the floor as neither women would have had the strength to have " neatly " placed it on themselves after such a savage attack. You're forgetting that June had a " psychosis " of a religious nature,,but nevertheless it was still a fragile and unpredictable illness.
Jeremy didn't frame anyone,,as he knew nothing about his sisters' illness,,neither did anyone else !