Abusers will use their family to plead their case and try to manipulate you into contact. These family members might not even realise he is doing this.
Also, his family members who don’t want to help him deal with his issues might try to pass it off as your responsibility.
It isn’t. You have every right to break contact if he is abusive. Your kids don’t need to see him if he is not appropriate with them.
People will try to make you feel guilty for standing up for yourself and setting new boundaries.
Either his brother is being hoodwinked by him or he wants you to take the responsibility for his brother off his back. Don’t listen. You are not the answer to another adult’s problems. Your ex needs to take charge of himself, or ask for proper help.
He is quite able to attend AA meetings or ask for counselling, but I doubt he even recognises he has a problem, as he is too busy blaming other people, in which case it would be pointless talking to him anyway.