Buying Duplex with Tenants already living there

[Barshay Graves]

Im putting together a deal for a duplex that already is fully occupied.  I have to live in one of the units since it will be an fha deal. 

Now the current owner says we can't settle until the first lease ends which is in September which will slow the entire process down. 

Why would this matter if I will be the new owner? Wouldn't one of the tenants have to leave when I say so? 

Anyone deal with a similar situation?