[landlord-us-ny] Tenant Demanding A $20k Buyout

Location: New York

Background:

• The Purchase: Closed on a two-family home in Brooklyn, NY, earlier this month. I currently live in one of the units.
• The Decision: There is a downstairs tenant of 4 years. We had the option to have the property delivered vacant but chose to inherit the tenant because the prior owners assured us they were in good standing and always paid rent on time.

The Issue:

• The Bait and Switch: The day after signing the purchase agreement, the tenant called to complain that the prior owners failed to pay a promised buyout. The tenant stated we are no longer allowed in the unit and must only communicate through their "lawyer."
• The "Lawyer": The prior owners contacted the tenant's supposed legal counsel. On a recorded call, this person demanded a $20,000 buyout (which the prior owners never agreed to). When asked for their NY State Bar number, they refused to provide it, simply said they practice in NY, and threatened to "see them in court."
• Current Status: The tenant has not paid any rent since I took ownership. I no longer want them living in my building and want them out.
• Prior Owners: I am in ongoing discussions with the previous owners, and they are amenable to providing a lump sum to help rectify the situation.

Questions for the community:

• What should I be thinking about and preparing for right now?
• How should I begin the NYC eviction process given the unpaid rent and hostile behavior?
• Should I involve the authorities regarding the suspicious lawyer refusing to provide a bar number?
• How should I handle the lump-sum offer from the prior owners to ensure I'm protected?