Hello, Should I start a legal business in order to start investing in real estate ??

I can't really speak into the actual legalities and logistics of it all just b/c I am not well versed in it...however, I did learn a lot about how it functions just by reading up on the lawsuit files that are posted publicly online.  

Is it legal for homeowners to sell the property without me knowing?

I wasn't sure if that was legal, let alone possible. 

If the building has a single legal address most of our carriers would consider it to be one building with two units.  

Last week, I received a Legal letter (from a lawyer) that I owe $2500 dues in HOA and requesting to pay it and failure to pay will result in lien on the property.

first position is always best... and fractionalized mortgage interest or DOT interest are legal in many states.. in many states like Oregon for example its not legal to have multiple beneficiaries.. without doing a real estate paper offering ( mini PPM).. 

While it might technically be legal, it would set off all kinds of red flags for the next sale.

I know in general wholesaling can be legal, but from what I understand and have learned, it's a very extreme fine line.

)                           -   Gross Monthly Operating Income              32,642.00 Monthly Operating Expenses Monthly Property Management Fees                   832.00 Repairs and Maintenance                1,000.00 Real Estate Taxes                5,241.00 Rental Property Insurance                1,959.00 Homeowners/Property Association Fees   Replacement Reserve                2,000.00 Utilities                1,291.00  - Water and Sewer    - Gas and Electricity    - Garbage    - Cable, Phone, Internet   Pest Control                   155.00 Accounting and Legal                   150.00 Advertising   Monthly Operating Expenses              12,628.00 Net Operating Income (NOI)   Total Annual Operating Income            391,704.00 Total Annual Operating Expense            151,536.00 Annual Net Operating Income            240,168.00 Capitalization Rate and Valuation   Desired Capitalization Rate 10.00% Property Valuation (Offer Price)         2,401,680.00 Actual Purchase Price         3,100,000.00 Actual Capitalization Rate 7.75% Loan Information   Down Payment            620,000.00 Loan Amount         2,320,000.00 Acquisition Costs and Loan Fees              60,000.00 Length of Mortgage (years)                          30 Annual Interest Rate 4.970% Initial Investment            680,000.00 Monthly Mortgage Payment (PI)              12,411.76 Annual Interest            114,527.10 Annual Principal              34,414.02 Total Annual Debt Service            148,941.12 Cash Flow and ROI   Total Monthly Cash Flow (before taxes)                7,602.24 Total Annual Cash Flow (before taxes)              91,226.88 Cash on Cash Return (ROI) 13.42% The property is being given to me after completing 40 year certification (updated plumbing, electrical, parking, most units are decently remodeled.