My stepson has been living with us the last six weeks in violation of our lease.. he has worn out his welcome for a variety of reasons.. we contacted the police today.. they came over and suggested he leave asap but informed us that our lanlord would have to evict him and that can take 30 days here in Michigan

Yes, he is "living" there now and you can't just throw him out. So you or the landlord has to evict him to do it legally.