It has 3 units, an additional dwelling unit in the garden level, and 2 garage parking spaces (which I've come to realize are quite valuable where the property is). 

There is some additional information that wasn't mentioned in your post above which sheds a different light on the situation.  1.

There are cheaper one’s in D/F areas but I would be careful as those can create a laundry list of additional issues.

I suspect it was two or more months on 1 bill in addition to what we pay for common areas.

Additionally, you may wish to speak with a CPA as to whether or not becoming an S Corp is the right decision – they can assist with reducing self-employment taxes.

A smart kid would say  NYET.

If you feel ambitious, you could try a BRRR strategy adding additional equity to the subject home and then taking equity out of it to pay off either the HELOC or if you decided to the refinance the primary residence. 

Although he is a banker, he thinks having the ability to operate as a broker and place loans with 30+ other lenders, in addition to his bank, is the "best setup."

Creating a catalogue of info and answers for the general benefit of those in the future in addition to the poster.

Any additional advice is helpful.