Aaand posted. It's a bit late at night so I probably won't finish the NPC in time, but the basic ploy is...

Rhinecliff laced the tea with a mild sedative, the sort that would feel more a consequence of a food coma than anything else, but would induce a deep, undisturbed sleep. The teapot he used was designed for that sort of purpose, and he did not lace Duchess Agustria's tea.

He plans on making either or both of the twins into sleeper agents, in the most literal sense, where upon a particular code word spoken, they will basically pass out. This will be accomplished by one of his mages, who'll be doing the work on them after they fall asleep in the carriage. In future hijinks, this will serve as a way for his favorite overworked changeling to have a new convenient individual to shapeshift into for the purposes of sneaking her way into the Wizard-Queen's circle.

Of course, if his words alone would be enough to caused the Skybound twins to focus more on looking after themselves and distancing themselves from the mess that the royal court will soon be, great!

For now though, kids gotta eat.

Also, definitely gonna have Rhinecliff chat with Willowsteel some time.