I have a vaccant home in NJ I have a homeless guy living there The house is up for sale and when people look at to buy he chases them out of the

This person is a trespasser.  you can go to the house with a police officer and have the person arrested for trespassing and then resecure the home.  If you cannot do this because you are in Florida you can use an "agent" by way of a power of attorney to act on your behalf.