I commend him for showing restraint because things could have escalated to an unnecessary death. Next, I agree with you that he should distance himself from this woman, even if she did not instigate the assault upon your brother.

However, he is his own man and probably got some internal battles going on due to his experience being in prison among other things, so perhaps it would be best to not get into any arguments over what company he needs to keep. I am sure he knows that you care about his safety and well being, but may not be emotionally ready to hear you nor whoever else telling him what he needs to do.

In all, he is alive and I am sure things will calm down between the both of you, if it has not happened already.