Lease agreement (big) discrepancies

[Richard Keiger]

I have a fourplex under contract. (Yes, I am a newbie...). 100% tenant occupied. Seller reported all long term unexpired leases and gross annual income $44,280. I received the lease agreements. Two are expired. Rent amounts are all different than reported, but not much less. Gross annual income reported on their Schedule E is $6,864 (Not a small difference!). I'm going to speak with the tenants today to find out what I can. 

Can anyone give me advice on how to proceed? 

Thanks in advance :-)