Disclaimer: My knowledge of this topic extends only to the states I live in or am licensed in. 

After closing, we discovered that for about 5-6 of the properties, tenants had been granted "sweetheart leases", well below market rates, extending through 2027 and beyond.

I offered not to raise a rent and if they extend, they could cancel any time to buy their house.

I'm new to RE too, but done my due diligence in reading on extend on the subject matter, and if I was the OP (still have not done my first deal), I would secure the deal, if its really such a great deal with 50k spread, in my mind I think he could get 15k wholesale deal to another investor and he does not have to do anything more than sell the contract, then after you have done a few of this and cash in your pocket, I would start with rehabs and rentals etc

They extended one loan a couple times and even gave me some more money. 

If extending for a longer term I would simply write the longer term, particularly if you are adding different terms.

We've had to keep extending closing for weeks because his communication is almost non-existent.

It all comes down to Costs... but keep in mind that a full roof replacement, should give you a new Warranty on it, and extended lifetime and lower insurance costs too!

A place my extended family could come and visit me at and be comfortable sitting in the room.

This exclusive buyer agency/agent contract is also restricting the buyer to only one agent until the contract ends which I think is unethical, the buyer also seems to have no right to choose how long(duration) the contract can be which I think is unethical too.