Jamie Lang BBC One and SundanceTV have ordered a third and final season of Sister’s “The Split,” created by BAFTA and International Emmy-winning writer Abi Morgan and produced by Jane Featherstone (“Chernobyl”), Lucy Dyke (“Black Mirror”) and Lucy Richer (“Small Axe”), with Dee Koppang O’Leary (“Bridgerton,” “The Crown”) boarding as lead director.Unspooling in London’s high-end divorce circuit, “The Split” follows the lives of the Defoe sisters, Hannah, Nina and Rose, and their imposing mother