Buying a Duplex to Occupy 1 Unit, BUT both Units have tenants

[Nick DiTommaso]

I have been actively seeking to purchasing my first home, and I am specifically looking at duplexes to live in one unit and rent the second unit. I came across a great looking duplex, in a great town near me. The price is a little above my liking but has been on the market for 7 months so I think I have some room to negotiate, but the only concern is that BOTH of the units are tenant occupied. 

I did some research and found the seller's info and was looking to contact him, most likely by mail, to speak about the lease agreements he has with his tenants. 

Has anyone experiences a situations like this OR know how to pursue this type of situation? I have never come across this type of scenario when learning about rental properties.  My guess would be to wait until one of the tenant's lease has ended to obtain a unit if I was to purchase this duplex. 

Thanks!

-Nick