How can you compare Jeremy to a suicide bomber? This man snapped over losing his job and house, so decided to kill himself and take many people with him. Sound's much more like Sheila if you ask me
But mass murderers don't appear out of a vacuum, as you would be well to understand with Bamber, Kehoe and Bain. It is years of unbearable tension for them and the trigger to execute their plan might be the one last straw which breaks the camel's back, such as Bain crashing a motorbike, Kehoe's wife's illness or even Nevill's mobile phone not functioning.
Sheila was not about to be kicked out of Moreshead Mansions and in her more lucid periods must have known that she would be well provided for long term.