It's hard when a gambler already has a misconception of what gambling really is and it's usually this misconception that makes gamblers fall into addiction unconsciously, and their mistake is always about assuming that gambling can be used as a place to earn while the facts about gambling can never support the intention and purpose of earning because the name of victory in gambling is nothing more than a “possibility” which in addition there is absolutely no certainty and any guarantee to ensure that you will be able to end the session with a win.
Yup, that kind of misconception as they think that they can quickly make money if luck permits them, they will keep on pushing and digging for that luck to com forward and let them win decently, though most of the time, even luck permits them they tend to keep aiming for more instead of taking that advantage to quit and enjoy their earnings.
I think in the end it is just a matter of time, because as you said they are difficult to tell which sometimes your suggestions and input can make them feel annoyed which in turn causes problems, so it is useless if we care too much about them because they also do not care about themselves and their own safety. On the other hand it is good to tell or advise them or direct them to things that can prevent them from bad possibilities but in the end it is difficult to make them really believe in our words and suggestions, which in the end yes as I said above that maybe this is just a matter of time which over time they will also definitely feel or experience the bad effects of treating gambling in the wrong way.
It's good to provide advise, but there's no assurance that those people will listen, even how close you are to them there's still a big chance that will just follow whatever they think is better for them.