That depends on the law in each country, but in most civilised countries an independent adult has to be present at a formal interrogation.
yes
You have to be 18 to sign a contract without a parent.
18 without a parent. 14 with a parent.
14 or older without a parent.
16
18
You have to be 18.
18
You have to be 18.
14 or older
The custodial parent.
No.