We own a rental house in Suffolk county in NY. We have had a yearly lease with a man who had his mother co-sign, for 2 years. He had moved in with his girlfriend and their young child. They have had a rocky relationship, with her moving out and returning several times. Now he moved back with his mother and cannot get her to leave. the lease is up for renewal in January. He would like to renew but wants our help in getting her to leave. She has threatened us with evoking her squatters rights. What is our next step?