He was off sick from his magistrate's job. Jeremy looked round at them:his mentally ill sister,a dejected June moping around going through the motions of existence, and then the twins,full of life..how could he possibly justify doing away with them? Well under their mother's influence they would grow up damaged,and it would give Colin a clean start,not to mention bequeath Jeremy the smart London flat he so prized.
Steve,,Neville was advised to steer clear of his magistrates position for the time being because of the hastle he was getting from a previous case. I doubt if he'd have told June of his fears,as he kept pretty well everything to himself.
I would have imagined that if Jeremy had looked around at each member of his family,,that he may have gathered that there was something in the wind,,but you didn't ask questions like that in the household. He wasn't weighing things up in a sinister way at all,,and must have thought it was something to do with Sheila,,,as usual.