I have quite a bit of experience with addiction through friends and also through family.
The hardest thing to deal with is watching someone you love self destruct. You know the beautiful parts of this person. You know how wonderful they can be and its hard to watch a tiny pill, pile of powder or pebble sized crystal be stronger than them.
But the bottom line is that tough love is the answer. You as a family have to agree to be his strength and do whats best for him because he has no strength and can not make good choices for himself. It sounds as though he needs to be commited to rehab. If HE signs himself in then HE can sign himself out. If his next of kin has him committed then the facility have more ability to hold him. At this point he is a danger to himself, his kids and his girlfriend. That needs to be addressed. Preferrably by professionals.
If you can not get him into treatment then you need to set some hard and fast rules for him such as no cash and be prepared to see him spiral downward. As hard as it is to watch, it is HIS life and HE has to be wiling to make the changes. If your parents are going to be weak and give him money, they need to understand that doing that is just as good as dumping the pills in his mouth.
Recovery is a long and hard battle. Addicts usually have to give up everything-their friends, places they go, social events.. because these are the places they find support for their habit and people who can trigger a relapse.
Its a long hard road, but it CAN be done. He just wants to have to do it.