Looks like we have an accord of sorts, then. We don't need to work out exactly how we'll play it before we do it. Exactly whether Sebastian will go the full manipulative dirtbag or not, I'm not quite sure. God knows, though, I'm not letting him have a moral epiphany when he realises he's come to love his adoptive son after all even though he thought he was only in it for the money and realises just in time to save him from his kidnappers [/ever_Disney_plot_ever] or anything like that.

Also, don't worry. Sebastian isn't telling anybody he thinks he might have been involved - it might be good motivation for supporting Matthew, so he can quietly contain the truth... I'm guessing it makes more logical sense for Matthew to issue a distress call (or have a witch-y NPC discover him and raise the alarm) than for Sebastian to initiate anything.