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.
I think that's his own concern to know what to do. If I am in his shoes and no one is feeding me, I owe no one any explanation of what I am doing with my money or declare my bitcoin to anyone be it my mother or father, because I know that future will tell whose investment will be more profitable. Bitcoin investment is private and not public.