When is a rental property considered abandoned?

[Nathan Richmond]

I have 4 individuals (2 couples) listed on a lease agreement that runs for 3 more months. One of the couples is moving out. I only know this because the other couple has contacted me.  The couple that is staying has been the ones paying the rent and utilities, so barring anything unforeseen, it should be business as usual. 

At what point is the property considered abandoned by the 2 that left? I'd like to legally be able to remove them from the lease.  While they are moving out voluntarily, they have told the couple that is staying that they still have every right to come back whenever they choose.

Has anyone experienced anything similar to this?