It is further my view that the agent has behaved in a manner that legitimately concerns you (to word it mildly) and is grounds for you no longer wanting to work with her. 

I don't think many here in less tenant friendly states appreciate how it can be having an unevictable tenant drive down your property value.

It's not behaving in a way that BP has taught us to look for the deals on the market, because anything listed is being snatched up by out-of-town investors.

With nowhere for the water to evaporate to, especially with the grout already placed, the pre-mixed mortar behaves the same way it does in the sealed bucket, which is to remain wet.

How can I be the best mediator and get these people to behave like adults?

You may be having trouble with banks right now because they are tightening their lending requirements and minimizing loans. 

The previous owner has trained them to behave a certain way and that has rarely matched the way I do things.My instinct is for you to let the tenants know politely and firmly (in writing) how you will be handling and managing the property and that the rents will be raised to market level.

Remember that renters aren't owners and don't behave the same.

Or will be have to pay taxes on the difference of the market value?

During the House Hacking period I will be having my roomates pay the mortgage while I save up enough money for a down payment on another property then keep snowballing off of that.