Somehow the hitman thing sounds plausible to me. A hitman (who didn´t know the layout of the interior of the farm properly) - no way, couldn´t have happened, not with three grown ups and two children and not at all at that low price.
Jeremy alone: no way. Too many possibilities of it going wrong with three adults - one might escape, even two might escape. Too daunting a task for Jeremy alone in the middle of ths night. I don´t think he was that "brave".
However, I have said this often: Jeremy AND a hitman, I can see that - and in that case, the price seems more realistic.
Sorry, just something I can see having happened, and it would explain some things that I struggle with in both the Sheila did it scenario (in lack of a better word) or the Jeremy did it sc.