My brother is a gambling addict. What's best kind of treatment for him?

If your brother will commit to some kind of treatment it needs to include Gamblers Anonymous attendance. He needs the support of other gamblers. He may also benefit from a family type of meeting, where everyone who has enabled his gambling and has been hurt by his gambling come together to let him know his gambling loss safety net is gone. As family members you will need to deal with the issues that allowed you to enable his behavior.

If your parents will help to pay for treatment there are many treatment centers around that treat behavioral addictions. It will take some research to find a suitable facility. Your brother should be a part of that search. He needs to demonstrate his commitment. To get started you could search for gambling addiction residential treatment.