She wants to sell the house to me for only what she owes on the house, so it could alleviate some pressure from her financially. 

I have been running the rental calc over and over again on different properties and I am not getting the return that every expert talks about.My next game plan is looking for SFR that may have an in-law suite or full basement to even Air BNB

If she doesn't provide the letter and is just trying to manipulate you with the threat, she can get her own air filter. 

Less pressure.

Growing up  I always wanted to be a fighter pilot for the air force. 

But with the relatively low CAP, Heloc would be a better choice for this property to avoid unnecessary pressure on the negative cash flow. 

Air Bnb?

If I sold my rentals tomorrow, I would still have clothing to wear and air to breathe.

Really up in the air at this point.

(local area puts these more appropriately at $725-$750/apartment as-is)* 2 brick buildings built in 1970, separated utilities, W/D hookups, central heat/air, no major upcoming CAP EX other than minor parking lot repairs* Expenses around $8k per year for trash, landscape, snow removal*Taxes currently $4300, will raise to $13000/year after purchase* Insurance $3,200/year* 10% assumed maintenance/Cap ex @ $810/mo*10% property management * 5% assumed vacancy @ $405/mo (growth region w/ high demand actually averages around 2-3%)With my financing that I think I'll get (20% down for 30 years at 6.25%) here's my calcs:*Current rents = 20% COC return, with $1700/mo cash flow*$725/unit rents = 25% COC return, with $2,140/mo cash flowThoughts?