Some of the specifics are credit score, DTI, signed lease agreement, and whether or not the lender accepts rent (house-hack) as income.

People with good credit scores can even be denied.

Depending on the lender and program your biggest hurdles might be credit score and income and time in job. 

I screen animals and then assign a score to determine how much to charge.

For almost any kind of permanent rental/investment property financing (whether Conventional, DSCR, or local bank), you are going to need a decent credit score to qualify.

@Devon Shives What's the plan to help the mrs improve her credit score?

For me A or B grade means that you can get a tenant with a 700 plus credit score with an income well above the minimum threshold. 

Meaning any of your Helocs can be closed or reduced at any point if any of your banks feel you are over leveraged, miss a payment, credit score drops, even by mistake it happens all the time.I would get rid of the Helocs and put some cash in your bank so you can use that versus a Heloc. 

For the 2nd applicant, her credit score shows 770.

:Class A Properties:Cashflow vs Appreciation: Typically, 3-5 years for positive cashflow, but you get highest relative rent & value appreciation.Vacancy Est: Historically 10%, 5% the more recent norm.Tenant Pool: Majority will have FICO scores of 680+ (roughly 5% probability of default), zero evictions in last 7 years.Class B Properties:Cashflow vs Appreciation: Typically, decent amount of relative rent & value appreciation.Vacancy Est: Historically 10%, 5% should be applied only if proper research done to support.Tenant Pool: Majority will have FICO scores of 620-680 (around 10% probability of default), some blemishes, but should have no evictions in last 5 yearsClass C Properties:Cashflow vs Appreciation: Typically, high cashflow and at the lower end of relative rent & value appreciation.