I'm Sami, here with only one kid: Dorcas Meadowes. Cas is in Sirius's year, so they've at least had classes together. She probably thinks Sirius is funny, and tries very hard to avoid incensing him in anyway; she's seen more than her fair share of Marauders' pranks :) She's pretty friendly, so it's not out of the realm of possibility that they've run into each other.
Cas will probably be a bit more leery of Lisa, only because she's one of the time traveler's. Cas's mum is a muggle, though, so they would have something to talk about!
I'm feetxofxmud on AIM and sodisarmingdarling@gmail.com