Out of State Motivated Seller Can't Get Live-In Son to Cooperate

[Daniel Elson]

New agent needs help. Listing expires March 2015. The owner wants(needs) to sell but her son lives in the basement and is collecting rent from the tenants in a single family home (renting out rooms). Tenants are more cooperative than the owner's son. Very difficult to show. One time the son said I was trespassing and said he could have pulled out [a gun] on me. 

House is in Queens Village, NY. I was told that she only owes $200k+ on the house. 

Where can I find info on what to do?