My son used both last year for ninth grade. I was amazed at how much his writing improved and how much more he understood with the literature component. What he really liked was how things were explained. He also liked how the reading load wasn’t too heavy because the concepts are taught through a majority of short stories and articles instead of novels. When they do read the novel most of the concepts have already been introduced so they go more in-depth. It really helped my son to understand the motivations of some of the characters. Considering his autism this was an enormous breakthrough for him. I think if your girls do the same subjects at the same time you might want two books but if they don’t they could share a book.