If I discovered that a couple who has rented from me for four years robbed me, do I still have to give them 30 days’ notice before I can get them out?

To avoid a defamation suit by them, be very careful in alleging they robbed you [say something like "I have been told that you were responsible for X"]. You can give them a three day notice to cure their action [violation of the law, breach of the lease] and then sue for unlawful detainer. You probably should also give them a 60 day notice that the lease will not be renewed. If you have solid proof they converted your property, tell the police.