No way,nugs. Although Jeremy appeared to look,and be grown up,he was still irresponsible so far as the business side of farming and all that it entailed,and he certainly wouldn't have even thought of going all out to slaughter his family. It's not something you do on a whim.
The person who carried out those murders was positively unbalanced,and could be forgiven for not knowing or realising what they were doing,and it wasn't Jeremy.
Sheila had always been the thorn in the side of her mother,and sadly it remained that way on the day that Sheila and the boys were dropped off at the farmhouse as both mother and daughter were immediately embroiled in yet another of their usual " spats ".
Did you know that even Neville couldn't calm such situations because June had the upper hand ?