In brief, she's told him she wants to separate with a view to starting divorce proceedings. He is refusing to leave the house. My friend feels she can't leave the house herself as a) she has been given legal advice not to be the first to leave and b) more importantly, she is concerned that if she leaves (with their DC) to go and stay with friends or family, her H will accuse her of kidnapping.
The point (and the reason for the impending divorce) is that her H is quite unstable. I am genuinely concerned for her wellbeing, mental if not actually physical, if she stays in the house with him. At the moment she is sleeping on the sofa (he refuses to be the one to do this) in an unheated room, quite nervous about going to sleep in the same house with someone who is behaving in a very aggressive and unstable way.
What can she do to try to get him to leave against his will? Is there anything, short of some kind of injunction? Her lawyer has told her (though she hasn't yet heard about the latest eruptions) that it is quite common for separating couples to stay in the same house, sleeping apart, while things begin to be resolved, but I do not think this is tenable in this case. Her H is aggressive, unstable, and has begun to threaten her with custody/finance battles etc.