After a written report, a hearing from the parties, full Board members may authorize legal action.Also on the first notice:"Your tenants were advised on [day / time] that they were permitted to move into the building Monday through Friday, between 9:00AM and 5:00AM, no weekends and no holidays."

Am I correct that I'm going to be the responsible party?

In addition you won't have another party dictating terms for you as to how you'll need to pay. 

After doing that I would offer cash for keys, in an attempt to get them out and make both parties happy(ish) with the situation.

I don't think NAR/CAR realized they back-doored themselves when they started providing data to third party sites.

May you live to be a 100 and invite me to your birthday party.

Definitely check on the disqualified parties and related transactions restrictions.

Building in the numbers a third party company, whether it be a prop man, maintenance person, or a landlord assistance company, is a good idea.  

The notice identified the interested parties as the property owners, Resmae Mortgage Corporation and GE Money bank.

By the post, it sounds like they have increased their demands (noting it is now a different party).