Jean Smart will succeed the late Diane Keaton in the “Family Stone” sequel, “The Families Stone.” On Wednesday, Searchlight Pictures, the film production company behind the new movie, made the announcement of Smart’s casting. “Welcome Jean Smart to The Families Stone,” they captioned the Instagram post. Fans took to the comments section to share their excitement for the news. “Hope someone’s polishing my tombstone because OMG I have died and gone to heaven,” said one user. “i’m sat. filming hasn’t even started yet probably but i don’t care i’m so seated,” added another. “HOLY MOTHER WHAT A GAG!!! I cannot wait! One of my favorite Christmas…