I do remember 2 boys 2 girls going to an mansion because something happened to the dad. They are locked in the attic and one of them dies. They witness the mother banging another guy. She is only thinking of herself and says she is getting married with the guy. the kids argue with her and she leaves.  in the finale they kill her in the wedding telling her to eat the rat or mouse which leads her falling to her death. The movie end with the kids walking from the mansion.