Wait a minute... I've read this almost half a year ago. It may not have been in english, but I remember this one. It doesn't end very well for the girls. Not well at all.
Though for as gruesome as it does get, I don't know if anything will top that guro I stumbled upon which began with the young girls dying from ultra constipation (one girl dies when her younger sister tries to help her by eating the stool out of her colon).
Awesome, looking forward to this. I wish more horror movies were as gratuitous and nonstop with the sex and violence as this series is.
I recently read a manga called Bloody Maiden which reminded me of these. A bunch of girls get naked on an island and get murdered one by one. It has pretty good art and violence, but it's still a shonen manga so there's only a few uncensored nipples, and of course no necrophilia.