Housing prices are high, mortgage rates are high, and competition is fierce so revenue is way downIt’s one thing if you bought a while back like many of us did, so your cost basis is much lower.

If you buy properties with little/no ability to drive value then you'll rely on appreciation and mortgage paydown to increase your equity.

Each mortgage we have about 250k left on.

MANY things can affect the title to a property, not only issues that are specifically recorded as a public record like a mortgage.

You must report rental income on Schedule E and can deduct rental expenses like repairs, maintenance, property taxes, mortgage interest (allocated between personal and rental use), and depreciation for the rented portion.

If the property requires rehab, the Realtor and/ or Mortgage Broker will suggest applying, for a FHA 203k Loan.

I would pay them whatever the sale of my property yields, minus any taxes incurred due to not taking a mortgage out.

You would want to look for an owner that has a loan through a bank or credit union or one that has no mortgage. 

If your rent ends up being comparable to your current mortgage, it might not give you the cash flow flexibility you’re hoping for.

I do not understand your remark as related to the DSCR loan.  2 ADUs are not allowed by f/f conventional financing but is not always enforced.Fortunately if you stay with the current tenant without a refi, by the time you pay principle it is likely the rent will have increased enough to absorb the increase mortgage payment.