Ok... I think the issue deserving precedence here is your friend and her daughters' safety. Keep in mind that beginning divorce proceedings will NOT guarantee an end to domestic abuse. In fact, there is a good chance that a man with some obvious issues is going to go ballistic when he finds out the person he has been beating into submission would try to divorce him. For safety's sake, I, personally don't think she should be in any close proximity should she choose the divorce option.
I also think your friend needs to get away from the abusive situation immediately. Being true to marriage vows does not mean enduring any kind of abuse, nor does God expect us to. Your friend needs to remember that she is entitled to basic human rights Biblically and legally. Maybe the abuse has escalated beyond physical into the emotional and verbal, and your friend's self-esteem has plummeted to the point that she doesn't believe that about herself. But, surely, she believes it for her daughters.
You note that your friend has been ''a victim of a poor upbringing.'' Staying in an abusive situation also makes her daughters victims of the same. She has a moral and legal obligation to keep her children safe. Her first step, I believe, is to value herself and her children enough to get out. She won't be the first woman to find herself a single mother with no money.
Now, perhaps what your friend needs rather than advice are options. Support/ advocacy groups and women's shelters are available to provide safe lodging. They can also help with employment, transitional housing, and also legal services. I note that your location is UK, but the following websites may still be helpful. She probably shouldn't access them from a home computer or anything that her husband could monitor. It's also important that you as her friend educate yourself, and realize that in helping your friend her husband may aslo retaliate against you. Be safe! She is not powerless, the situation is not hopeless, and with God you will overcome.
National Domestic Violence Hotline
www.thehotline.org
National Coalition Against Domestic Violence
www.ncadv.org