Charlotte Richie, who plays Oregon in Fresh Meat, and Tom Stourton, who is one half of sketch double act Totally Tom (regulars on Live At The Electric), will take on the two key characters - the world's worst brother and sister.
Siblings, which is produced by Bwark Productions - the company behind The Inbetweeners - revolves around Hannah and Dan; a pair of obnoxious, lazy, self-centred, underachieving, incompetent and occasionally depraved siblings who cause chaos and disaster wherever they go.
Joining Ritchie and Stourton as guest artists across the series will be Stella Gonet (Hacks), Tracy-Ann Oberman (Give Out Girls), Emer Kenny (Badults), Steve Brody (Life's Too Short), John Dagleish (Starlings) and James Lance (Teachers).
Executive Producer Simon Wilson says: "We couldn't have wished for two more brilliantly gifted comic performers than Charlotte and Tom to bring Keith Akushie's hilarious creations to life."
BBC commissioning executive Chris Sussman adds: "The cast are brilliant. The scripts are very funny. The director is great. All we can do now is try not to mess it all up."
The six part series is currently shooting in West London and will be shown on BBC Three in Spring 2014.