Carolers.
A singing group of eight is called an octet.
The group that walks through the streets in the neighborhood singing Christmas carols is typically referred to as a "caroling group" or a "Christmas carolers." This tradition dates back to medieval times when groups of singers would go door-to-door spreading holiday cheer. Caroling is a popular activity during the Christmas season and is often done by church groups, community organizations, or simply a group of friends or family members.
Generally it means a group of people singing (or carolling) Christmas songs
Quartet.
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.
A acapella 5 man singing group would be called a Barber shop choir.
The choir.
Trio
A singing group of three is called a "trio."
the ronnettes, frosty the snowman
It's called a quintet
A quartet is a singing group of four.