I apologise in advance as this is my first ever post and may get complicated. Basically my DF is in an abusive relationship and I have no idea how to help him. DF and DSM have been living together for around 6/7 years, their relationship has always been volatile but it seems to have deteriorated in the last year. Around the end of 2016 DSM was diagnosed fibromyalgia and decided to give up her part time office job for good. She was already suffering from COPD and heart disease and has now developed a codeine addiction.
Since leaving her job she has no income, so my DF has been working 3 jobs to support her habits, pay bills, save for christmas and birthdays and take care of all their pets.When he isn't working any of his 3 jobs he's ferrying around DSM and her granddaughter as she refuses to drive, decorating, gardening, food shopping, and looking after my DSis etc, meanwhile she spends ALL of her free time in her bedroom playing PS4 online with strangers.
DF does everything for her and she repays him by treating him like crap. She kicks him out regularly and holds over his head that she owns the house and everything in it. She calls him an alcoholic, throws things at him and tries to hit him, slags him off to everyone because he can't take her out on nice dates to fancy restaurants and on holidays abroad conveniently leaving out how many hours he works to support her. She accuses him of cheating constantly, talks to him like shit, tells him to kill himself with his antidepressants and she pulls vile stunts to hurt him.
Most recently on christmas day she waited until my dad left to take myself and DSis home and she and DS-Sis had their dinner together, leaving him to come home and eat christmas dinner alone. They then interrupted him eating his dinner to sing happy birthday to DS-Sis. She has no interest in being around any of our family, ignores DSis, refuses to attend family events and holidays and kicks off when he takes my lonely widowed 86 year old great grandma out.
Today DSis told me when DF went out to walk the dogs at the weekend she sat in her bedroom listening to DSM and DS-Sis slag him off knowing that she was sitting in the next room and could hear them. I feel something needs to be done, the behaviour is disgusting and must surely constitute emotional abuse. I also worry about the kind of example this is setting for my sister with regards to relationships now she's getting older.
DF won't admit he's hurt by her although I know him well enough to see it in his face. I don't think he'll leave her as he has nowhere to go and could end up homeless but I cannot continue to watch him burn himself out for someone who treats him so terribly.
Aibu to go over and confront her about her treatment of him, or even just how inappropriate it is to discuss their relationship issues in front of my 11 y/o DSis?
I guess this mostly just turned into a rant but I really don't know what to do or say to help him anymore 
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