https://www.lipstickalley.com/threads/destiny%E2%80%99s-child-vocal-coach-beyonc%C3%A9-was-the-only-one-with-a-good-voice%E2%80%94kelly%E2%80%99s-vocals-were-air.1475662/"
Beyonce was the only one that came with this phenomenal voice. Kelly's voice was little more than air. With LeToya, I thought 'she will take a longer time to learn to sing in a pop or R&B style' because she had a very naturally high placed voice. I had to teach her to sing in her "chest" voice."
"When the record company initially decided they didn't want a rapper they were going to kick LaTavia out of the group. I told them 'this girl has been there from the beginning, and she deserves a chance'. I asked them to give me six months – just six months to work with her, and I did work with her. She worked the hardest out of all them because she was the weakest. I built her into a singer and, yes, she can sing"
"I taught them harmony... how to build cords. I taught Beyonce how to instruct – so she could teach the chords she composed to the others."

"On the subject of whether LeToya and LaTavia contributed to the vocals on the Destiny's Child and The Writing's on the Wall albums, Brewer is blunt.
"This is true for some of the songs. To save time and money the record company, producers and managers often had Beyonce lay down the background tracks. All four girls learned the tracks in order to perform them live, and we went over the songs extensively. It wasn't that they weren't capable. It was about saving time and money." In the music business, time and money can be precious commodities. "I can remember sitting in the studio waiting for producers for 10 or even 12 hours. They were supposed to be there at noon and showed up at ten at night." Even when they're late, however,
producers often show little patience for performers who would use up more than a few hours of studio time."

And lastly:
"He even notes that it was Kelly, not LeToya, who failed to get admitted to a performing arts program that she, LeToya and Beyoncé applied to during high school"