The kidnapping attempt wasn't Sethos' style (nor, I think, is he stupid enough to order the manhandling of someone he's tried so hard to woo). But, if not him, then who? Bertha comes immediately to mind - she could easily be Sethos' partner or second-in-command. And SHE wants Amelia dead. Slowly and painfully, if possible, which would make a rather violent and painful kidnapping attempt decidely her style.
Now, the 'children' know almost nothing of Bertha.
And then there's that reading teacher, with the burly servant and the offer of tea.
Oh, very uncomfortable.
(on a side note, the possiblity of a partnership of some kind between Sethos and Bertha is amusing, if only because they both want one half of the Peabody-Emmerson pair alive and the other dead, but they don't agree on which is which.)