Tenant moved out, New cousins moved in!

[Michael Henry]

I'm managing a property in Milwaukee, WI and I found out three days ago that the tenant moved out, of course, without paying the rent. When I pull up the house I see someone washing a car and the backyard.  I get out of the car and walk to the back of the house and the guy says "you must be the landlord," I tell him that I am the property manager and asked him where is the tenant, he starts to tell me what happened and why he was there. In short, his cousin had an emergency and had to go down south for a few months and she asked them to take over the place and they can start paying the rent next month. Interesting, I was never notified of anything.  

I walk through the house and all their things are moved in. I told then that they had to apply and it was up the landlord to keep them here under the circumstances.  I spoke to the Owner and after I told him what happen he said he wanted them out!

I call the cousins up and told them the good news, and this is when it is great to be a manager. 

How would you handle the situation based on the information provided? And what would be the next step you take?