I have just signed a lease and sent in my first month's rent for an apartment in Chicago, along with three other roommates and our respective cosigners. Today, after having sent in the check and having been approved 100% for the apartment (and we have been told "it is ours" and it is "off the market"), we were informed that the former tenants would like to stay. I was under the impression that they have already told the landlord that they were going to leave by August 1st and that the apartment is OURS. Is this legal? What can I do about this?