There's no individual credits for songs on the LAP booklet, this wiki page just took what they wanted from the general album credit which also have Lynne Fiddmont, Marcos Loya, Marilyn Martin, Nadirah Ali, Rose Banks and The Andrae Crouch Choir credited as "background vocals".
It's pretty clear that not all of those people are in the song and is pretty clear that there's a choir in the song (and the only song to use one on the album), so why would they need Niki and Donna?