In the order they appear in for the intro:
Grog: The way Travis plays him on the show, Slytherin. I can easily see him going Hufflepuff or Gryffindor in a less violent AU which calls for fewer questionable choices, though.
Keyleth: Gryffindor, maybe Hufflepuff, but her self-sacrificial tendencies at the beginning of the series and the way she loses her temper strikes me as more of a Gryffindor thing.
Percy: Ravenclaw in a “the de Rolos are all alive and flooding Hogwarts” AU. They’re a Ravenclaw family. As he’s seen on the show, though, definitely Slytherin.
Pike: Gryffindor or Hufflepuff, but I see her going more towards Hufflepuff.
Scanlan: Slytherin. Since I seem to be listing secondary houses for everyone, his would be Ravenclaw, but like. He is the epitome of the non-evil Slytherin, come on.
Vax: Hufflepuff. Gryffindor maybe, but too, ah, complacent with peace and quiet, I think. Maybe a Gryffindor at the beginning of the series, but as he is right now, Hufflepuff.
Vex: Slytherin. Ambitious, opportunistic, charming. Ironically enough, I’d alternatively put her into Gryffindor, but you can make a case for basically every house with her. But Slytherin is definitely my first pick.
Tary: A Ravenclaw who really, really wants to be a Gryffindor and as such would probably end up there.
Tiberius: Hard Ravenclaw. Gryffindor or Slytherin on his worse days, but obviously intended to be a Ravenclaw.
Zahra: Ravenclaw or Slytherin. Probably more of a Ravenclaw, though.
Kash: That very grumpy Hufflepuff friend.
Allura: Ravenclaw. No ambiguity there.
Kima: Gryffindor. Same.
Gilmore: I’d put him into Ravenclaw personally, but you can make a compelling case for every other house.
Will gladly sort other characters if requested. Also, shoutout to @kymal for this excellent A+ listing of other AU tidbits.
Overdressed & Underappreciated 