The man probably trusted his family, which is a really natural thing to do, though sometimes it turns out to be a mistake, like it clearly did in this here, as the son proved untrustworthy, unfortunately.
If a man trusted his family, he would give them access to his wallet. And then he would not have been poisoned by drugs, and he could have died.
Having a lot of money makes you a target primarily for your family and friends, so it is very important to keep this data secret.