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.
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?
I think he owes them no explanation, even as his family, it's not their business how he spends his money especially when they didn't secure the job for him, the family are just ignorant about Bitcoin investment cause if they were, they should know that Bitcoin as an asset is held for long-term to bring more profits in the future and not something that would get one rich immediately.
I'm really suspicious of his family members cause why would they even be forcing him to declare his assets, the man was very wise enough not to do so and if I were in his shoes I'll relocate to another town for a while so they won't plot against him and force him to declare it on gun point, I said so since they're forcing him against his wish to declare his assets.