If I transfer BTC to a friend/family, they now know my wallet address, correct?
Yes, they can see the address(es) which sent them bitcoin.
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The simple answer is if you don't want anyone knowing about your other transactions, then never reuse addresses and be careful about spending change.
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I think if you just want to hide your balance from a family member who isn't a tech guy, you can just transfer a small amount to another address and then make a second transaction to the family member.
This first transaction will most likely "hide" your total balance, and people wnt be looking past transactions unless they really want to track you.
Ofc that is not the best way to have privacy, and the best is to use a bitcoin mixer.
But I think it depends on how much privacy you really want to achieve.