Re: committing Suicide
The fact that the father lives with her brother should have nothing to do with her telling him. I think that you have an obligation, both Islamically and legally, to tell someone when your friend has threatened suicide.
To be honest, it was a mistake to tell her husband, because it sounds like things have already gotten so bad between them that this may just make it worse. And this is definitely something he can and probably will use against her in court, should he petition for custody.
Custody does not automatically go to the father, in most cases, it goes to the mother, although it would be better if she had at least a part-time job, or some means of supporting herself. You need to encourage your friend to be proactive and, if she's not going to think of herself, at least think of her child.
I would also suggest that she see a lawyer and look into protecting herself and her rights. Documenting her husbands threats against her is also a good idea.
I am not advocating divorce, but it sounds as though this guy is first of all verbally abusive, and secondly has either made up his mind about divorcing her, or enjoys mentally torturing her.