This is why it's good not to store all your bitcoin in one wallet. It's better to use two wallets, you keep the large amount in a seperate wallet like a cold storage and keep some amount in your online wallet, so that when such thing happens like this, you can show them your online wallet.
What if he has different wallets and decides to show them the one with little coins inside they will still not be contented with the amount they will see there as they will feel that he has mismanaged his funds.
It's not advisable to declare all your bitcoin hodlings to anyone by force be it your family members. What of those his brothers that are into physical earnings, did they declare all their asset and funds in the bank to the family?
No one should be pressured to declare their asset to anyone but the brothers and the family were literally concerned that he is not doing well from their own perspective since they haven't seen any physical improvement based on how people feel that when you start making money from your investments, you will now start doing things that will convince them that you are doing well for yourself. And moreover, he has already told them that he's into bitcoin.
It is up to you with your concern about your privacy and safety. The more people know what you are doing, the more risk that your privacy will be leaked more. It can affect your safety too, and if you are worry about privacy and safety of your fund and life, just don't tell anyone about your investment in Bitcoin.
People who are into cryptocurrency in general should be cautious of their privacy and security but this people are literally your family members who are concerned in what you do and want to know if you are making a headway from it.