I am pretty sure they will need a better margin down the line if they wanted to stay in this game. 

Problem was the sales price and my dad wants to stay in the apartment he lived in and wanted to stay, but can't make an agreement with the doctor where he can stay somehow.

Jim Cummings if you get a warranty deed, your title insurance stays intact.

Now they might argue their tenants stay for many years so vacancy is almost nonexistent, but I am skeptical of this kind of thing.Is there any major metro in the country that is not a Detroit or Chicago where 10+ cap on a C level duplex or something is achievable?

I have had a number of (non-RE) issues with PayPal and advise anyone to stay away from them.

If staying he needs to pony up what she is owed, and sign a new lease with his name only.

I believe it's zoned as residential, but I don't want to evict the tenants, I want them to stay and lease back to them.

Those are some big goals for your first 3-6 months, but definitely achievable if you stay focused and put in the work.

I generally just talk to them 60 days before the lease expires this gives them enough time to decide if they want to stay or move out.

An estoppel certificate will show you what current rents are at.Last thing you want is to read in the fine print the landlord has given the tenant a place to stay for a huge discount over a long term.