I'm going to assume they are letting you use your schedule C/E from your other rental for income verification OR you simply make enough otherwise to cover any debt to income ratio needs.  

You mentioned on hand reserves and that is an additional amount that is also raised upfront. 3 months of projected operating expenses and debt payments is typical for stable properties.

You will pay a higher interest rate from a lender than you will on your LOC.Neither of these funding resources are designed for long term debt, you'll want to have an exit strategy.

To answer your question, your Debt to Income is what is evaluated when purchasing multiple properties.

A 15-year will bump up your debt service by $400-450/month.

My debt to income ratio is too high, because they are holding the debt from the loan used to purchase the Airbnb against me.

Financing the debt at below market rates would ensure that it'll make business sense for you not to refinance that debt for quite some time, keeping his payments secure. 

I am having similar issue with this also.Add on to that, I am looking at my income and debt ratio also.I got some SFR on mortgage and some fully paid off and they are all on my name. 

Never heard of itits a form of ownership rights.you buy a property from someone and you deed them a life estate.. they live there for the rest of their life once they pass they no longer have the right to the property and you then take over possession.. it is common for those getting on in years  and their heirs don't want them to have to move and it generally means no payments maybe only utls.. 

The NOI plus the debt payment doesnt exceed what I make now at my job.