[chosen]

So they both live here, and her husband has been cheating with three women? Is he in the British army? Are they residents here?

I think she needs to get legal advise about how she can protect herself and her daughter. If he has been violent and has threatened her, then a restraining order may be a good idea. Whether he will take any notice of that is another issue. If he is in the army then I would suggest she finds out who she can go to within that organisation to make sure they are aware of his threats and violent behaviour. Hopefully they will take it seriously and act accordingly. It may also be worth her going to the police and telling them of his threats and violence as well.
If the worst came to the worst and he because more threatening and she was afraid for their lives, then a women's refuge may be needed for a while. Or she could go to a family member or friend who lives away somewhere.

As for the divorce, there are many divorce solicitors around. Maybe find one on line.

She may need to move away at some point where he cant find her. Maybe even go home to be with her family?