Technically there is nothing wrong with it legally or morally, in and of itself.
However, some people might not see it that way.
Yes providing that it is not a sexual relationship and your parents/guardians are OK with it.
Their parents or legal guardians.
You cannot choose your foster parents or legal guardians.
If the minor (key fact) in question is not emancipated and his/her parents are his/her legal guardians, then no. If the minor (key fact) in question is not emancipated and his/her parents are his/her legal guardians, then no.
If your parents are not your biological parents and have adopted you and made themselves your legal guardians then they would have to have adoption papers or it wouldn't be legal.
Yes, unless otherwise ordered by a court.
18
No.
Someone else can only sign for postal mail addressed to you if their name is on it as well, or if they can prove that they have your power or attorney or are legal parents or guardians.
No, the child's under-age parents are the legal guardians of the child.
No, turning 18 does not automatically emancipate someone. Emancipation is a legal process where a minor is declared legally independent from their parents or guardians.
Are your parents or legal guardians aware that you don't know the answer to such a simple question?