Shimming joists so there is no movement in them and decoupling work but it is harder to achieve  then other types of noise control.

Staying in control in things you are responsible for will help things go better.  

My goal was how could I control $5M worth of real estate in 10 years?

Maybe find another investor interested in the same area and go in and take control of the area.

He is taking the two current owners to court in an attempt to regain control over the property, force a sale and rid himself of the mortgage they current owners were suppose to pay. 

I know am not in the best position to advice you on because am from a completely different region, west africa to be precise but i do know each state in the United State has its real estate guidelines and requirements and of course you need to sit and pass the real estate exams for agents of the state you choose to practice before a real estate agent license can be issued to you.

The problem is the property's expenses are out control.

We simply want to unload it and take control of our money.

Sell the banks with a professional financing package and control the message and data they receive.  

I suggest you make the new lease M2M to insure you keep control of the property following the change in tenancy.