One important detail is that my brother currently lives with us, and we are open to having him stay with us if we do make a purchase as a renter to help cover our mortgage.I see our main options as the following:1) Buying an SFDU to live in, and "house hack" with my brother continuing to live with us and pay rent2) House hacking with MFDU.

Have 2-3 contractors look at the job and get written estimates on what it's going to take to finish the job, correct the mistakes, pass occupancy certification etc. use those estimates in your countersuit / mediation process. 4.

Make sure you have a lot of ducks and all fo them in a row. 5 year estimates on revenue and expenses, full business plan, licenses etc etc all in place before you go in.

Define roles, financial contributions, profit-sharing, and responsibilities in a detailed agreement.

From there you assess if month to month cash flow deficit is okay, that's really such a small detail of it.  

Duplex appraised 380 (super ****ing low ball) brings in an estimated 3,900 a month in rents. buyer agreed and SIGNED addendum to purchase at 397,500. day of closing they dont show, tell us they didnt know what they agreed to pay over appraised value and are trying to get us to accept 386k. my agent had me lock in our month to month long term tenant to a year lease for THEIR lender and now they pull this.. they have only 5k in escrow account.. my agent wont reduce his commission from 3%-2% to help bridge the gap. suggestions?? 

Alternatively, you could continue growing as a personal account and then swap your account to a business account if/when you want to. airbnb.com/account-details allows you to pick if you are an individual, business, or other entity.

Quote from @Charles Evans: There are websites that estimate market rent, but they can be off quite a bit.

Here are the details of the property:Property Overview:Location: Texas2 lots, 2 warehouse buildingsFinancials:Mortgage: $4,897/month (balance: $530,000)Insurance: $830/monthProperty Tax: $1,800/monthBuilding 1:1 tenantRent: $7,570/month12,000 square feetBuilding 2:3 tenantsTenant 1: $2,850/month (5,000 square feet)Tenant 2: $1,793/month (2,500 square feet)Tenant 3: $895/month (1,250 square feet)The property was appraised for $2,200,000 three years ago.Given the current rental income and expenses, the cash flow is decent, but my family friend is looking to explore options that could potentially yield better returns.Would it make sense to:Sell the property outright and invest in higher cash-flow opportunities?

Details on the duplex:Price: $385kBuilt: 2012Size: 2674 sq ft (1333 each side). 2 story, 3B/2.5B each side w/ 1 car garage & driveway for both, fenced backyard both sides.Interest: 5.49%PITI: $2,698Current Rent: $1,350 but could be brought up to ~$1,600, maybe $1,700Yearly Property Tax: $8,340 (I don't pay any on my side while I live there so $4,170)Upgrades: Vinyl floor in kitchen of both units, new AC (central HVAC) on vacant unit, roof done 2016.