What would be your advice for such if they were to be your friends as a caring friend who want them to not get financially drained in the process?
Same old tips that he shouldn't gamble for him not to be drained financially. Because if he's going to gamble continually, he'll lose a lot of money and might not take it on his own.
These friends of ours will listen to us a bit but they'll still follow their ego to do what they think is right and what they are up to.
If they continue to gamble and never listened to your advises, stop advising and stop following him. Do your own thing and leave him alone, let him realize his mistakes soon.