I can understand how difficult this is for you . My son has been addicted for a long time to cocaine and other drugs. In my experience it has caused me many dilemmas . I’ve covered for his behaviour , not told certain people the whole story etc. I also moved in with him to help sort him out again having to tell certain people a different reason for my staying with him . I think if you tell your dad your going to upset your brother and if you don’t you could upset your dad . You can’t win . It’s going to have to be your call and I know it’s hard but maybe at this stage with the possibility of your brother getting the help he needs maybe I would let your brother decide who he wants to tell. It’s his illness and I think you sound like you wouldn’t like to break the trust at this stage . Well done on your support it’s difficult. I’ve been doing the same now for a very long time . I wish you well.