Wait, didn't in the story you say that Jane Morgan died? So then how can her 'step-siblings' be willing to kill their mother if she is already dead?
And she can't have the money until she is 18. It's like in the Series of Unfortunate Events. Violet can't inherit the money until she is 18, and so Count Olaf is after her right? Jane can't have the money for real, until she is of age to get it, so therefore her siblings could kill her, and get the money. Is that what you mean when you say that they would be willing to kill to get the money?