2 Duplex package..Need help with analyzing!

[Tanner Carson]

i am practicing  deals just want to get opinions!

I called a "for rent" sign to discuss how much this little cabin cost to build... just looking for information. We ended up discussing his investment career and him and his wife, now older, have moved out of state. He offered me his whole package of 20 doors. But as a newbie i narrowed it down to a 2 duplex package, so 4 doors. all units are 2/1 and i havent seen the inside. both need new roofs which he knows. so he already said he would cut 20k off because he is trying to get out of this area and these are currently off market. to be listed at the beginning of the year.

his offer 280k total

currently 100% occupancy and has carried over 90% occupancy for 10 years (or so he says)

Insurance- $1656 a year for both buildings 

Property tax - $2202.3  & $2393.4

current rents are 650,650,650, 565

he offered to seller carryback up to 35k to help me with downpayment

i have a family friend as the VP of a bank and have been discussing many deals over the past two years as i try to learn financing.

15% down required for investment property.

at 280k my payments would be 15 yr fixed   2000

                                                           20 yr fixed  1730

at 200k my payments would be  15 yr    1450

                                                             20 yr    1240 

I played with BP calculator at a purchase price of 265 and came up

with a monthly cash flow of 116.36

and cash on cash ROI of 13.36%

I would love to get help with this!

Thanks in advance