Chorus
Choir
noun
People who join in a chant group are people who are in a chorus or choir.
がっしょうだん
The reading for 合 is pretty weird. It's a がっ instead of a ごう. Just imagine a bunch of people in a chorus singing "ga ga ga ga gaaaa!"
合唱団員は、みんなで手を繋いで歌っています。
The members of the choir are all singing hand in hand.