I hope you have verified that there will be sufficient equity and that you'll be able to qualify (either DSCR or Conv) for a takeout loan or cashout refi for the hard money.

While a detailed log is often sufficient, adding additional documentation can strengthen your record. 

But, something to add that you have to understand is that a 3-4 unit has to be meet the FHA self sufficiency test.

I need to ensure that the rent-to price ratio will sufficiently cash flow as I intend to hold at least 5-years before acquiring any other real estate.  

She may be getting alimony payments sufficient to allow her to qualify on her own.

Not sufficient for individuals' identification always, though.

Instead he/she claims that his/her invoice is sufficient.

You have the problem common to a lot of people getting started; wanting to invest but lacking sufficient capital.  

If you want to leave your IRA intact and avoid penalties or taxes, consider other options such as:HELOC (Home Equity Line of Credit): If you own property with sufficient equity, a HELOC can provide funds for a down payment without tapping into your IRA.Personal Loan: Depending on your credit, a personal loan may be an alternative.Seller Financing or Private Lending: Look into creative financing options for real estate investors, such as seller financing or private lenders, which can help with down payments without needing to use your IRA.

I am still not sure which one is sufficient for me to do.