I have no wonder or worries about this because I love them and I trust them so much. We are living together and sharing together, so it is not matter if they also know about this.
But as other members here said also that trust only people that you can exactly trust, not other people who may cheat you from the back.
Maybe he has some problems with this.
But if this is about the condition that as he said about his family (know nothing about crypto), I agree with you that he may also at least tell the family about it in common. So, if something happens, at least he can leave something good for his family.
But once more, this will depend on what kind of family he is in.