Legal advice. That's what you are calling what you've told me? "He has no rights", is a statement, made by you, reflecting your own personal opinion about my brother and his girlfriend.
It would appear that you have little understanding of how this all works. From a legal OR a biological perspective.
Everyone KNOWS who the mother of the child is, because she is the one who carries the child and gives birth to him/her. However, because said mother could have had multiple partners (and being realistic, if she's as bad as you claim, the likelihood is that she did), it is impossible to state unequivocally that a particular partner (i.e. your brother) is the father w/o DNA testing.
IF they had been married, the law presumes that your brother would be the dad. Because they were NOT, the child has only one parent until the court establishes who the father is. Until the court establishes that your brother is, actually, the biological father (via DNA testing), your brother has no rights. None at all.