Lisa Gregory is a pseudonym for Candace Camp who now writes historicals.
They were a sensation--the #1 group in America. Behind the glamour and the glitter lay the tears...
IRIS: The talented lead singer who thrived on the cheers of the fans, the fast money, the fame. But there was a hunger raging inside her to be a superstar...and to be free of Madeleine, the mother who loved and controlled her with equal power. Now Iris was scheming, lying, and running wild: a "bad" girl forgetting the sisters who cherished her and running headlong toward seduction, sin, and the worst mistake of her young life.
DIANE: The gorgeous backup singer who blindly adored her sisters. She didn't see the betrayal or the passions that would rip a family apart. And when the terrible truth finally turned dreams to ashes, she ran from show business to marriage, searching for the happiness she craved. Instead, fate would sweep her into sudden, unexpected celebrity, a tragedy that could cost her everything, and the arms of a man who promised one last chance...for love.
Above blurb taken off the back of the book.
I can't remember reading it, so it must not have been remarkable.