Help! Abuser?

My nieces’ current boyfriend who she lives with has been causing a lot of dysfunction in our family and from what I have read he seems like he could be a Narcissistic Abuser. Anyone who has some info would be greatly appreciated. He came to the rescue to take my nieces mother (my sister) in after she had major surgery and then shortly after had multiple fights with her and kicked her out. He is still very verbally abusive to my sister and blames all of the family problems on her. He had said that night that if my sister even "opened her mouth" he would kick her out and he did, even when my sister was agreeing with him on that certain matter. He recently has looked my mother in the face and told her how much he loves my niece, myself and my mom. Then we heard a message he left calling my mom and myself horrible nasty names. He refers to his house where my niece lives with him as "his world". Seems like he is trying to alienate my niece from her family. Thoughts?