Your parish is probably going to need to purchase at least enough editions of "Choral Praise" ( https://www.ocp.org/en-us/collections/dg/63 ) for the choir members if you want to continue to do what you've been doing. Otherwise, there's good advice above.
I believe that Carol's husband's approach is a violation of copyright law because derivative works of a copyrighted work must be made with the permission of the copyright owner of the original work.
I suppose if someone wanted to improvise a harmony to a copyrighted song and didn't write that harmony down in musical notation and didn't distribute it, that would skirt the law.
But you cannot rearrange a copyrighted song without the owner's permission.
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