I need advice. 😔

So my brother has had an on and off again girlfriend. Well long long story short. She does not know what she wants. One minute she likes him the next she doesn’t. Well a month and a half ago she told him she didn’t want him hanging out with “joe” well he said he didn’t want her hanging out with “Jane”. They agreed. Well a few nights later she said she was one place then posted a tweet about being at another. He left work because she was lying to him and caught her in the lie hanging out with “Jane”... they got into an argument and she said she was leaving and he said if she left then he was done and to give him back the engagement ring. She gave it back. The next day she started dating her other ex. A month goes by and she starts calling and now two weeks later she says she’s pregnant with my brothers baby. She’s around 6 weeks. So it could be my brothers or the other guys. She admitted to him before she cheated several times throughout the three years. She has no job. The other boy has nothing to do with her. My brother has a house and a steady job. I’m only getting pieces of the story but things just don’t add up to me. Could she be using my brother ? What do we do to help him? He’s so hopelessly in love with her. She is making him stop talking to my family and I just found out 3 hours ago and haven’t done anything but be nice to her. I live 2 hours away and don’t see them often and she’s saying she hates me heck I haven’t spoken to her since Christmas didn’t even know they broke up until a month ago. And I never said anything about her. I’m so confused I don’t know what to tell my mom to do she is distraught thinking she will never talk to her son again or see her grandchild or what to do or say.she doesn’t want a job or tries to get one. She doesn’t clean or cook or do anything. We are a little concerned about how things will turn out once the baby comes.

What is the girl thinking? I was in a similar position but didn’t do any of this so I can’t even imagine what’s going through her head. What do we need to do as the family?