I suggest you do an LLC together and eventually put the duplex on that LLC

I eventually blocked all of them (I think).

I could buy a titled property, but they are all a 5 minute drive from the beach or further away.My plan is to put about $20k into the house, stay there on some long weekends, rent it out when I'm not there, and think about what type of house I would like to eventually build, probably something like a 5 bedroom / 5 bath.   

People move eventually and tenants that stay beyond their lease can always get evicted by an owner-occupied buyer so there is usually a peaceful transition during transactions. 

I am a physician, still working full time but with a serious plan on growing and diversifying my real estate portfolio to eventually have more freedom in my medical profession.

Focus on saving for a down payment and eventually buy a 4-plex with FHA financing. 

Eventually I want to invest in other states. 

She will be moving back with them eventually, does she not think her next landlord is going to call her last landlord for a reference?

Additionally, we all hear about you do deal #1, then deal #2, eventually running out of funding but you keep finding deals and eventually have to utilize hard money or some other means of funds.  

If you aren't confident in your knowledge of that specific market, find someone who is, and learn your market through them, eventually with their knowledge and repeatedly analyzing deals for yourself you will build confidence in your ARV's.