after you told your brother everything, and he didn't listen. forget it, let him find his own learning. but don't let that happen to you or your other relatives.
you do not need to be responsible for your brother's actions because you have already given a warning. such a scheme would not last too long. when they get enough money from people who join, everything will disappear very quickly.
just wait whether your brother succeeds in withdrawing profits or not.
Saying the user haven’t got to be responsible for his brothers action is an ignorance to the duty you owe a sibling. I don’t know but somewhere within our DNA or subconscious, we do hope our family members, relatives or friends that we do do care about don’t walk down the same road we did once or are way too familiar with to lead just no where.
I do understand that, when you try to teach a younger person or even an old person of something they feel they know too well about, especially one that has got some evidence to it, they build a wall about what they wish or hope to believe is true. The approach to it, create some relativism with it from what has been before. Let them get the clear picture and where it always ends, should they hope continue the part and you caution them enough to instill in them some level of curiosity and skepticism so they don’t get to invest big.
When it goes down, then they would understand and learn to trust in the things you know and experience have got to teach them.