How do I make my brother believe again?

Du can't really 'make' him believe. Sharing with him some signs that you've received/are yet to receive may encourage him to believe, but I cant assure Du that it will work. Du can also share with him some experiences others have had with him as well (as long as they're all true). That could also help as well. I cant promyou that your brother will start to believe again, but I wish the best for Du :)