My mother-in-law is wanting to sell a property that she is 30% heir in. 

@Anirudh Reddy you should NOT depend onthe cops to remove homeless people and squatters unless you verify the local laws and what the police will actually do.HOW are they getting access to the building?

What does your local laws say about how soon you can evict someone? 

Find a lawyer who specializes in landlord-tenant law in your state, and not only that, but who know the rental and property management business well.

Hope the laws are the same. 

But, you asked about a nonrefundable deposit - subject to the local laws, the agreement you make can be anything that the buyer and seller agree to.

Quote from @Victor Verano: Mid-term rentals are actually long-term rentals in the eyes of the law and should be treated the same.

I don't know NC landlord laws but we have great landlord friendly laws here in Austin and prices have come down significantly off the peak.

Let me share my story.As the title suggests, I received a house as a gift from my father-in-law upon getting married.

Check your local laws, but if it starts for Sept 1, tell them you need the new lease signed before Aug 1 because if it isn't signed, then they need to move by Aug 31 (or I guess the 7th) and you need to be able to get the place rented.