Lostmum I am so sorry you and she are going through this.
I agree with Reflexella focus on getting your sister to leave him. Engage with your niece, does she live with her mum, could she move out if she is 20?
I am sorry for your sister but I also feel angry that she has allowed her daughter to live with this horrible man for a number of years. I totally get she is the victim of this abusive man but she is also complicate in allowing her daughter to have lived with him.
Please don;t engage with him, I don;t think he will change. Focus your energy on your sister. Is she supporting this oaf financially? Imagine how much better off she would be (in every sense* if she cut him loose.
Tell her about Women's Aid.
www.womensaid.org.uk/
"Call us
Contact the Freephone 24 hour National Domestic Violence Helpline – run in partnership between Women’s Aid and Refuge.
0808 2000 247
[email protected]*
Please note we can not respond to emails by telephone as safety may be compromised. If you wish to speak to somebody please call the helpline number."
He has snot been violent yet but he could be in the future.
He is living off your sister, yet she is abused by him.
She must have lost all self respect, remind her she is worth so much more. You don't need to tear her down for any failures on her part, (much as I say I would be angry at her for staying I would not say it, unless I really felt she would leave him).
Has he made sexual innuendo comments about your niece, his step daughter? If so, that is a massive, massive reason to leave!
Tell your sister you are sorry you have made things worse by telling him some home truths, but that you know she is worth so much more than this, and so is your niece.
YANBU for being angry and upset and wanting to help. Focus your energy on getting her away from him. He doesn't need to just tone it down a bit. He nears to clear off altogether, he is toxic, your sister is worth so much more.