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.
Does it make any sense, to try to hide or cover up for what is bo body business, what I would like to know is the level of the bitcoin holder's responsibility, is he responsible and laying his bills or does he still rely on his brothers for help with bills even though he claims to have bitcoin investment, Becassine I don't see any reason or right for his family members trying to interfere in his personal life.
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?
The only person I can declare everything to is someone like my next of kin this is because if I am not accessible, he or she could trace and recover my Bitcoin holdings.
Apart from that, my asset is my business and I have no obligation to declare them to any family member, for any reason, something is wrong with the guy in question and he should know that it is not right that give his family members such impression of being irresponsible to the point that if asking him to show them his proclaimed investment.