What do you think, how they could work in DF-Chicago?
Larry Blaisdel is pretty much unchanged. He's met Buffy, and he's been affected by transformative magic. You can even say that his Weapons skill is a residual effect from his night as a pirate, the same way that Xander retained military skills from his army costume that night.
Edward Kendall's role is affected by the role that the Watchers play. Are they allied to the White Council? It's not impossible to envision such an alliance. It's also not impossible to envision a not so friendly alliance where the White Council feels that mortals should stay out of supernatural affairs while the Watcher Council doesn't trust mages enough to safeguard humanity.
You'd have to decide if Beatrice Kendall is part of on of the Faerie Courts or else make some decisions regarding her sponsor. I like the idea of a Dream Court with a Morpheus/Dream/Sandman in the style of Neil Gaiman at its head, and Beatrice having a complex relationship with it. Beatrice is likely to be a changeling, who is half human and retains he free will. It's possible that the nightmares she get is a tactic that is being used by Morpheus to get her to embrace her fae nature fully. It's also possible that her obligation to the Watchers is the result of some kind of binding Faerie bargain, made by her or by a noble of the Dream Court.
Kamila Khan works as well. It's possible that her origin is connected to Jared Kincaid, who is a human with demonic enhancements. Given that the Slayer(s) got their power from some kind of Shadow magic, there might be a way to connect it to Kincaid. It might also explain why the Slayer isn't supposed to kill mortals. Aside from the moral implications, it could also be interpreted as a violation of the First Law.
You'd also have to decide how Buffy is connected to Kamila. Did Buffy happen in the mid-90's? (this also affect Larry, since this might make him about 35 years old). Did every Slayer awaken? Are there hundreds, or just dozens. Is Buffy their "general"? Is she even still alive (since this would also make he mid-thirties). I personally like the idea of having "dozens" of slayers instead of hundreds, where the US might have a grand total of 30-40 slayers, and Kamila is one of them. I also think it would be cool if not all of the Slayers were good. Many of them might decide to use their powers for selfish purposes and be supernatural mercenaries of sorts. If that is the case, do Kamila and Buffy and the other "good" Slayers feel a need to bring the bad Slayers in?
Jason Drake's stats still work but he would probably be adjusted to fit in with the Dresden model of Werewolves. He probably works best as the same type of Werewolf that the Alphas are (and in fact, I used them as a template for his skills) which means his wolf form is a wolf, not a Wolfman the way Oz was. The good news is that his lycanthropy isn't infectious. You could give him a Hexenwolf belt if you want him to be more of a Wolfman, but that has consequences in the long run.
Henry Evans might get the raw deal in this scenario. His magic *might* impact his ability to use computers and he would be subject to the laws of magic. It might also make sense to give him the full White Council powers (full evocation, with Fire as his preferred element), with The Sight and make him a White Council member. Or you could downplay his thaumaturgy and make him more of a fire guy exclusively.