You could also negotiate the contract so that settlement would not occur until the tenants lease is up. If you do buy the house with tenants, be sure to have the security dseposit transferred to you at settlement.
One consideration from personal landlording experience - if you do purchase the property & keep that 6-month lease extended, be prepared for 1)anything to happen to the condition of the home 2) trouble to arise in rent payments 3) laws to lean heavily toward tenants in the eviction process, you don't want to end up with a squatter. So if you do move forward, make sure you & your agent carefully carefully carefully research the tenant, their credit & their payment history.
You may decide that with so many homes on the market to choose from, the additional stress of landlording may not be your cup of tea. Best of luck, NIcci@NicciHyatt.com