Oh gods. I can see this going in *so* many different directions.
First up, Loz is going to want to meet the dwarves Granny gets to service her broomstick, and then he's going to wind up concussing himself on a regular basis trying to learn all about magical engineering (or at least flying broomstick maintenance) from them. Maybe Loz will be able to get Granny's broomstick to go without bump-starting.
Then there's Yazoo meeting up with Nanny Ogg or Magrat Garlick, Perdita Nitt or even, gods help us all, Tiffany Aching. Yazoo is the one to really worry about - he'd be the one who'd sit down and *analyse* witch magic, and then turn out to be scarily good at it. Despite being male - or possibly because of being male (and frighteningly androgynous), since witch magic is all about edges, and Yazoo is very much on the edge between masculine and feminine.
Kadaj strikes me as the type who'd run off to Ankh-Morpork at the first chance; at which point he becomes a problem for Commander Vimes, Lord Vetinari, and Captain Carrot. All of whom are well and truly qualified to deal with him (I think he'd find Carrot hardest to cope with, although it would be fun seeing him try to out-Machiavelli Vetinari...)