There's a reason why a gambling addict don't tell tell families about their addiction, and a close friend should respect that. If you really wanted to help, better ask your friend's permission first before you tell it to anybody, especially their family.
The reason why they don't tell it to their love ones is that they are afraid of getting judge, instead of getting sympathy and help from them. Not all people have a very understanding families, mostly they've got toxic one that's why they do stuff that will get their families attention.
The only help they could get is from a friend who is willing to guide them in a different path that's going to cure their addiction.
For how long will they continue to judge him? To me a friend should try to help in whatever way that they can so keeping it a secret from the family to me seems like a wrong thing to do.
Even if the family wants to judge they would do that but it will be after they have successfully helped him get rid of his addiction and they’re are also some family that will still do it without an ounce of judgmental look.