What perspectives do Lady Macduff and her son provide that have not as yet found their way into this play about political intrigue and ambition?

Well, their concerns are more domestic than political. They are true innocents. They discuss what might happen if there were more "liars and swearers" than "honest men" without reflecting on what that might mean to people like them. Ross warns Lady Macduff of her danger, but she cannot understand it. If she could, she would have saddled a horse and been gone before Ross could go.