I've been seeing: AS-IS contract, Sub to addendum, Authorization of release, power of attorney.

What @Jay Hinrichs is saying is that if you go before a judge, and you show that these leases were signed for significantly under market value and signed just a few days before closing, there is a good chance the judge will side with you because it is an obvious attempt to pay less rent and take advantage of the new owner.I think your next move should be to contact an attorney in your area who specializes in landlord tenant laws in NJ, and see what they recommend. 

People need to realize to get class action status is near impossible in many instances and the attorneys make all the money.

Find an attorney whose specialty is evictions.

Surely the mighty NY real estate industry has stakeholders with deep pockets and an army of attorneys to work on this thing, no?

You may consider a business attorney familiar with your state or jurisdiction if you do not wish to spend the time to do it on your own.  

Ask your Realtor/attorney for help with this.

.), Hard or Refundable Earnest money & terms for that, broker representation, title company, attorney info, etc.Best wishes to you. 

And when you really need a complicated setup like this is when you're under attack, meaning you need an attorney to handle the case.

If the tenant fails to provide the landlord with the forwarding or new address as required, the tenant shall not be entitled to damages or attorneys fees under division (C) of this section.”