Crossly is the major domo at the recently-acquired von Lipwig residence (or Dearheart residence; the point doesn't seem well-established) on Scoone Avenue as well as Moist's valet. Mrs Crossly is the cook and housekeeper. These, along with Crisp, the gardener and handyman, seem to be a skeleton staff for a Scoone Avenue mansion, but the von Lipwig-Dearhearts are away on business a lot and Spike in particular won't be wanting to entertain the local gentry very much.
Crossly's most difficult task is getting the young master out of bed for important business at unholy hours of the morning (often with single digits). Managing the large house is less onerous for Mrs Crossly because it's so often vacant.
He approves of Moist's handling (with the aid of Spike and her dodgy crossbow) of the Patrician's guards' ignoring propriety. (Raising Steam, p. 250-252)