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?
Yes, there is a saying that goes "don't have all your egg in one basket". You know the nature of crypto that it can be hard convincing people about crypto if they've not seen evidence on you. So diversify your portfolio, you can have like two so it's safer when someone needs to see anything and you are not confident showing them your major portfolio, you can show them the lesser one.
But I would not be comfortable telling family and extended family it's not safe, it's not wise someone can calculate it and even know that you have certain amount of money but you are claiming not to have money you know issues, jealousy, envy might start from there and you might just be having unnecessary issue that you can you could have avoided if you just kept things to yourself.