The pilot is set in New York and focuses on three dysfunctional siblings -- played by Gellar, Molly Parker and Nate Corddry.
According to The Hollywood Reporter, Orth will play the playwright husband of Parker's character. Scott will play the ex-husband of Gellar's character.
Scott, currently starring in the Starz comedy "Party Down," previously was a regular on HBO's "Tell Me You Love Me."
Orth has appeared on recent episodes of "30 Rock," "Fringe" and "Canterbury's Law."
Stay up to date with the latest breaking news in the worlds of movies, TV and music by signing up for HitFix E-mail Alerts.