Should I tell her mother ?

[Heswall]

Very briefly, my brother has threatened, brushed past, roughed up what ever you want to call it his girlfriend.
This is the second girlfriend this has happened with, giving him the benefit of the doubt the last girl would get physical and he would respond holding her wrists whatever according to him. He has two children with the first girl.
So here we go again, she is 18 years old, had a baby first week in January, he's admitted to cheating on her too.

I am so ashamed of him, he did witness domestic violence as a child and his dad was a bloody bully but there's no excuse.

Back to this young girl, this is her second violent relatioship, her last boyfriend hospitalised her and her mother was not happy as you can imagine.
The mother apparently knows something is not right and gave the girl an ultimatuim my brother or her, she chose my brother, realises this was a mistake now. She has now convinced herself she cannot go back to her mums and is going to stay with friends, but I do not believe this for one moment. Keeps saying she loves my brother - I don't right now - what would you do for the best.
If she was my daughter I would want to know.
I'm worried about loosing her trust though.

I've sent a note to her mother and so we will see what happens next.
If these two were at A & E with an injured infant I might agree something more needed to be done but they aren't and it's not worth breaking down the trust for what might have happened and what could easily be covered up as an accident.
The baby is with her grandmother and if she feels the baby is at risk then she doesn't need to hand her back tomorrow i guess.

My gut feeling is that you must contact SS and, possibly, police!

You would never forgive yourself if something awful happened to the baby and mother!

Fucking hell having spoken to her mother, It turns out it her that's been hitting him.
So he is the victim, TWICE.
What on earth do you do to help ?

Hmm. She could still be in danger, and her child too. Very often, in abusive relationships, it's hard to tell who the "main" abuser is, when the victim retaliates in kind.

They are both clearly products of highly dysfunctional families, though, so I would treat anything her mother says with a certain amount of scepticism too: we see all over these boards how abuse victims' mothers collude with their abuser against their own child. It is the pattern for someone who keeps entering abusive relationships to have a parent who scapegoated them from birth.

Not saying this is necessarily what is going on here, but it is a distinct possibility.

The child's safety is paramount: the baby cannot protect itself. Hopefully, your brother and his girlfriend will eventually take control of their own lives and go seek the help that each of them needs.

What do you do to help your brother and/or his girlfriend? Listen to them. Offer what advice and pointers you can towards sources of professional help. Make up your own mind on who is the most vulnerable one being controlled by the other.