As the owner of our property, how do I terminate a lease agreement set forth by our property management company?

Without seeing either the agreement with your property manager or the lease beginning on June 1.  It is impossible to tell what your options are.  If you assume the new lease is valid then you are obligated through the actions of your agent.  May the agent have some liability?  Was the agent working within his designated powers?  May the new tenant allow you to terminate the lease, maybe for a small fee?  Are you obligated to pay the property manager his 3 months of management fees?  Maybe be depending upon whether or not he was working within his agreed power as property manager when he signed the new lease. As you can see there are a lot of questions that need to be answered and the answer will likely depend upon the specific language of the agreements.  I recommend that you contact an attorney and schedule a live consultation so that these issues can be discussed and your options can be reviewed.