I asked you why do you think they'd commit murder,for what reason ? I didn't expect a half-baked answer that meant nothing.
The "WHY" still has to be broken down, Lookout. We can't get an answer from the few who commit suicide after murdering. Some of the others may not know. Some may say that they heard voices -I don't recall it ever being mentioned that Sheila was one of that number. Some may say that they felt under attack.
Had there been any incidences of Sheila EVER having attacked anyone previously -and I refuse to accept that the marital spats fell in that category- the might be some credence to what you believe, but as it stands, all you appear to be doing is using her illness and adding everything, including the kitchen sink to the mix, to make her and/or June, guilty. Not so different from what Jeremy did, really.