Squidward auditions to be a choir boy, but only to be failed, and for SpongeBob to be chosen. However, he still gets in the choir but only as a page turner and not a singer.
"A Day Without Tears"
They are seen driving in their boat car. They gather regularly at their choir studio that looks much like a small church. After all of their practices, they have a season of performances at their usual open-air concert hall in Bikini Bottom.
In the episode "Choir Boys," they are first seen on a picture wearing different clothes that are the same as the clothes that Squidward wore. Also, they do not wear shirts in that episode, unlike Squidward.
Their mustaches are not real, because it is shown that when one becomes a part of the choir, they get a mustache.
For some reason, Squidward does not have a mustache in "Choir Boys," even though he was a part of the choir.