Who are the Ka-tet in the novel, Wizard and Glass?

Ka-tet is a group of people who are bound together by ka, or fatee. Roland Deschain forms two ka-tets, one in his youth with Alain Johns, Cuthbert Allgood, and Jamie DeCurry, as well as one as an adult with Eddie and Susannah Dean, Jake Chambers, and Oy the billy-bumbler.