Who is Caleb Mellon Swain and Letitia Vanderbilt Swain from Slapstick: Or, Lonesome No More! and what is their importance?

Caleb Mellon Swain and Letitia Vanderbilt Swain come from enormously wealthy families and live in Turtle Bay, NY. Neither Caleb or Letitia graduated from college, but they are described as well spoken, kind, and humble.