The Quincy families seem to be modeled a bit around western mafia.
So far as I can tell, it's still unresolved whether or not Quincy arrows destroy souls, and whether they had a war with the Seireitei. My personal vote on the matter is that, if they don't (which a fair number have been advocating), then either there was no war, or the cause of the war isn't fully understood by either side. In either case, we're assuming that there's been peace between the two factions for a while.
As for Quincy characters, I have no idea, save that an incidental character that I'll be playing has basic Quincy skills.