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All that I know are Icon For Hire and Call Atlantis.
Gospel singers for an event can be hired from several agencies. Examples of some agencies are Gig Salad, Charm Music, Liquid Strings or Chosen Events.
She has 2 brothers and they aren't singers.
Any quartet has 4 singers by definition.
yes
Back-up singers can work with any singer who needs background vocals.
a bunch of singers can sing any song together
Back-up singers can work with any singer who needs background vocals.
no
none...
Eagle scouts can be anything they want to be or can have any talent they want. -- There are a lot of former scouts who are singers, but doesn't look like Eagle Scouts. The links have lists of famous scouts who became singers.
An employer can hire or not hire based on almost any criteria they choose, as long as it does not violate any discrimination law.