I'm bolting in in the last ten minutes I have for the day before having to vanish again until tomorrow buuuuuut Charles and Theo should definitely drink and play cards sometime! Theo would also be very interested in Blackstone's illusions, and whether or not she could use them in her tent to make her more..."authentic" looking sometimes - it looks like him and Theo joined the carnival about the same time too!
As for Nic - he'd be absolutely fascinated by Blackstone. From the sidelines. Magic is pretty, but people and crowds are stressful ^^' but he'd probably be one of the ones that helps with Charles' horse as well!