They have a lease but are receiving a section 8 voucher which pays almost all the rent.

Make sure the voucher covers the majority of your rent. 

During the recession there was a time the city stopped giving out vouchers.

bought property in March 2017 - put 20% down150,000 downmortgage 375,000 interest rate 8.25% 2/1 ARMseller misstated financials - thought they were actuals but were performaswhen got into the property was expect 7800 in rent but wasn't the case 2 tenants had gave notice - both were TRA (temporary relief assistance) day of closingGuaranteed for 6 months instead of a yearHad 6 TRA tenantseach were paying 1550 per monthflooded entire basement - Repairs Complete1175 (2 rentals) newly renovatedOriginal list price was 1350 but dropped down to 1175 (stayed on market for 69 days) - 2 rentals3 other individuals were phasing out of TRA - 1 stayed (1175) - no evictions from November - Januarylost $15,000 from 2 evictionsbrand new roof 2017Mortgage payment: 4200 per month mortgage and PMI taxes and insurance includedNationstar - amortized commercial property for 30 years - 30 year mark fully paid off 29 years left on mortgage -after 2nd year variable interest rate (max cap is 10 1% max for year 2/1 ARM)( 3 Months Behind on Mortgage)all 6 are there 1 is moving out on the 30th Apartment 3Lonly 1 left on TRA (court last Tuesday) - was going to be evicted lives for 3 months - gave TRA voucher for 3 monthsNeeds to pay $18,000 backpay for mortgage companyFebruary 1st $4,200Needs about $25,000 and some reserve to handle certain thingsBuilding pays for itself - Total is $7100 - mortgage $4200 - cashflow $2900has a partner and he lives over seas - he wants his money backbought at 500,000 March 2017Appraisal: 600,0000.70 = $420,000 Cash out Refi MaxBalance is $373,000 on mortgage $1600 to renovate the unit - Used Security Deposits for Renovationsno reserves in the bankNeeds full $18,000 —back 3 months in Mortgage—Once February is collected will be $1,000 shortTenants - all separate utilitiesPay only $100 for lights in hallway - all baseboard heating - bring own AC unit for windowsRenovated 4 of the 6 unitsNEEDS: $142,000 needed to pay off investor - wants 12% return (until he is off the loan) per year he is on the loanhe already received $8,000 OWES him $10,000 $142,000 + $10,000 = TOTAL: $152,000Back pay on Mortgage $18,000TOTAL $170,000$2900 cashflow monthly Owner wants $900 cashflow monthly out of $2900Any suggestions would be appreciated on how to structure this deal in order to benefit the seller, as well as myself.Lease options?

I know having a good property manager that is skilled at placing and working with tenants with a housing choice voucher is crucial as well as obviously working with an investor friendly. 

That is a direct reflection of the decrease in the amount allowed for the section 8 vouchers.

Some want to spend $200k to $800k on a 80-100 unit building with a cap rate of 8-9%, they do NOT want to accept vouchers, and they do NOT want to use much money for rehab...

The tenant gets a HOUSING voucher, not a rent voucher.

The issue you are going to have is that a SEC8 voucher holder cannot rent from a relative.

It is fairly new (built in the 2000s) which is quite rare and will likely rent out to a voucher Section 8 tenant for around $1300-$1400.