Plenty of HMLs have a long-term product separate from their short-term products but they are distinct products.  

I feel your pain @Daron Williams First, find out if your problems can be repaired or if you have to go your separate ways.

If we do a cash out refinance, should the funds go in a separate bank account, and can we use those funds to actively invest in the stock market?

@Xiaoyan Liang I got a quote on just a furnace to have separate heat and it was not worth it.

I successfully converted a 2400 sq ft single family 3 bed/2 bath into a 2800 sq ft, two separate 3 bed/2 bath ADU, by converting a two car garage into livable space in Santa Barbara. 

And maybe a separate operating entity to manage the property you own as tic.There can be other options depending on entity structure.

You can ask for proof of funds or if he submits an offer real money in escrow (ie NOT a note or nothing-down).Willingness to put money at risk separates the adults from children in this business.

I would suggest trying to find Single Family homes where you can have separate living spaces (walkout basements, separate entrance) that way you get the comfort of a duplex without the price. 

That company must look and act like a true company, with all expenses and bookkeeping kept separate from your personal finances.

Two separate things...the code enforcement violations will actually be an investment in improving your property.Evicting a non-paying tenant will actually be a financially and emotionally rewarding experience for you.