Allison Janney is preparing to bid farewell to her beloved CBS sitcom Mom, when season eight ends May 6. She's in talks to lead a dysfunctional family, along with Annie Murphy and Ben Platt, in The People We Hate at the Wedding, from director Claire Scanlon and writers Lizzie Molyneux-Logelin and Wendy Molyneux. Family comedy: Allison Janney is in talks …