It would leave your net worth really skewed into one asset and class of asset. 

The seller does get benefits, but they aren't necessarily financial.

I want to give them the benefit of the doubt they are just struggling with staffing but now have seen some red flags that lead me to believe there might also be some type of deceit/fraud and possible financial trouble.

Brother B could be convinced to see things my way but has had some financial strains lately so it might be an uphill battle. 5)My mom is in memory care and did not do any end-of-life planning so my brothers and I are footing the cost of her care.

More than likely the asset will in a location where cap ex & management/operational costs are disproportionately higher and therefore your expense ratio will also have to be adjusted to a higher number.  

Turning a historic duplex into a high-performing asset while forcing $100k in appreciation is no small feat—seriously impressive. 

Although I'm seeing some great deals happen in 5-10 unit assets near the downtown and university areas.

Businesses are the opposite: their primary purpose is cash flow and while you can create a sellable asset, anyone who has ever tried to sell a biz knows it's a lot harder to sell than real estate. 

We initially allowed investors to manage these properties themselves and ran into a lot of issues that affected the integrity of the neighborhood which then affected the other investors and their assets. 

Each option has different implications, so choose based on your financial goals.