In "Our new neighbors move in yesterday," the last word is enough time adverbial yesterday, so the article of your preposition in may be omitted. Of course, in an information question, "into" also can be final phrase apart from an adverbial when its object is questioned by a wh- word: https://to32086.develop-blog.com/34825028/how-to-can-save-you-time-stress-and-money