Since I will have owned it only 3 years, the property value increase is minimal ($35K) and closer to $15K once I pay a listing agent and closing fees.2) Gift it to #2 son now and let him pay the Capital Gains tax at his rate (0%) when we sell next year. 

There should be other options, however with an LLC and fourplex - yes, DSCR is by far most likely to be your best option unless you do the heavy lifting with local banks and credit unions (and these are increasingly not great options for this type of stuff as they move painfully slow and are under lots of regulations and restrictions)2) I haven't yet reached out local banks, but seeing the quotes from brokers makes me wondering if Banks may be better? 

., which creates a great opportunity to leverage real estate for attracting travel nurses and other medical professionals.

Option C (selling) simplifies finances and provides a large lump sum (~$270K), but triggers significant capital gains taxes, potentially increasing Social Security taxation and Medicare premiums.

Also having a higher proportion of revenue generated through the residential component of the building does make financing easier. (3) The exception to the 80% rule I abide by is when the commercial space is leased to a credit tenant with a proven & sustainable business  or where the space presents the opportunity to attract a neighborhood amenity F&B operator (this is most beneficial in instances where you have a larger localized portfolio where these commercial tenants can positively impact the value of your overall residential portfolio).

Monthly rent is $1,850 and plan to increase next year.

LTR, MTR and STR work in most larger markets (~top 30-40 cities by pop, or be proximity to metros/attractions/employers).

Lender will make sure you dont open any new trade lines or have increases on your balances.

Improved DSCR: If a company’s DSCR has increased significantly since the original loan was taken out, it may qualify for better interest rates or terms, making refinancing advantageous.2.

Do you feel, given the current state of the market, the risk is increasing in this type of investing?