Use and Enforcement: Easements

My question involves an easement in the state of WA. My mother has an Easement on the driveway of the house to the front of her. The easement was written into the Sale of the Land and is on the Title. The person who owned the house passed away and the house was sold to a man that is pretty "angry". My sister lives with my mother and she has friends that visit. My mother has friends that visit. I visit. There isn't any speeding on his driveway/easement but he has started coming out and harassing anybody that drives up it. He has posed No trespassing signs and insists that unless we are "family", you aren't allowed to go up the easement to get to my Mother's house. He says he is getting a lawyer and will Sue my mother but I'm not sure that he has a case. My mother isn't using her property as a business or anything like that. Any thoughts?

Use and Enforcement: Easements