They would be called a soloist.
A "solo".
solo acapella. solo because of one person, acapella because there is no music.
A soloist.
a Duettt :)
Two people singing together is known as a Duet.
scat singing? if that's what you mean
Solo.
A person who goes around singing at Christmas is often called a caroler. They typically sing traditional Christmas songs while spreading holiday cheer in their community.
The person who leads the prayers is called a 'cantor'.
they have the same singing voice it is one person.
The lowest singing range a person can achieve is called the bass range, which typically spans from E2 to E4 on the musical scale.
The "cantor" is the person who does most of the singing in synagogue.