Once the family member receives the bit coins for low fees, how do they buy a loaf of bread?

This is nothing new.  You currently purchased the coffee with USD that you earned and was paid to you after tax was deducted.  You would have the same accounting and tax liability if you had purchased Euro in 2000 at .90 USD.  When you would go use them today and got 1.40 USD you had a capital gain of .50 USD.   Same works if you lose, you will be able to deduct a capital loss.  You will be able to pool the purchases and come up with a yearly weighted average to simplify.  Similar to buying shares over many months.

If you have the financial backing, why would you need to prove it to anyone?   Please explain

What happens when Amazon acquires $6,000,000,000 worth of bitcoins and doesn't sell them.  Just hoards them?   I don't think the market cap of Bitcoin is large enough currently to be able to service Amazon.