One of the big reasons I believe that God allows us to experience drug addiction and other things like homelessness, rape, etc is so we will know it. To have lived through challenges and come out stronger means you have developed strength and character.
The best counselors and helpers are the ones who have been through it. A former drug addict can understand what other addicts are going through and can help them.
Now it is up to your brother and his girlfriend to have some sort of epiphany. Maybe your family can arrange an intervention.
They used to say you can't force someone into treatment however these days they believe (rightly so) that you just get the person into treatment by force by hook or by crook and once they are in and start to come down from the drugs they start realizing things and can't get more drugs so they are forced to begin dealing with their feelings.
Good luck and I hope they come to their senses soon.

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The political system is broke and it's a joke.