Most of the time, people make mistakes first before realizing that they are wrong. Very often to happen that some people have fallen into investment scams because they never listen to other's advice. Very unfortunate, but never let it happen to your siblings since you already have an idea about the Ponzi scam scheme which is likely they are into now. They might argue with you OP but must have to be firm in your position and convince them that they are wrong and help them understand how real crypto investment works.