@Frankie Lotrec if you have an existing loan on the property and you plan to legally convert from a 4 unit to 5 unit , you should check the loan documents because you’d essentially be converting it to a commercial property, since 5+ units is considered commercial and subject to different appraisal approaches and so it would rule out the property being considered for purchasers utilizing residential financing.  

I'm assuming you have one lease covering both tenants and not individual leases.

https://www.amazon.com/couch-covers-pets/s?

Do you already have some kind of pre-screening questionnaire setup to weed out undesirable tenants?

My husband and I currently have a rental home in CA and want to utilize a 1031 exchange to build an ADU on an existing, non primary residence in FL.The existing Florida home is co-owned with our son, and this is currently HIS primary residence, not ours. 

Quote from @Roger Paschal: Quote from @Quentin Hollis: I'm currently working on my first real estate deal and will be buying a property subject to the owners existing mortgage.

So far, nothing.The point is that I believe people spend a lot of money, time, and effort protecting themselves against a non-existent threat.

Sometimes less is more and just taking the step to buy one more might be better than selling your goose that laid the golden egg in the existing successful house.

A 50% LTV on a $120K house at 7%, 30 year Am results in a $400/mo interest payment.The cashflow on your existing duplex goes to $1,000 per month, but now you can buy another just like it so yoru cashflow goes to $2,000 per month.  

I currently have a pre-tax retirement account with employer match and a Roth IRA invested in the stock market.