Jenny is being played by Devon Woods. Devon has also been seen as Young Tara on Showtimes The United States of Tara.
Kathy is being played by Dannika Northcott. This young actress has a nice list of credits to her name, including recurring roles in ABC sitcom, In the Motherhood.
And the new Spike and Ian are.... Jake Vaughn as Spike and Britton Reeder as Ian.