Since everyone is throwing out their guesses on who's who, I'll join in:
Killer - The "I'll do the cooking"rule woman. She slept with 3 men so... that's that. And the way she held that knife screams "I'm a fucking psychopath".
Sadist - The glasses girl or (though this one is unlikely)boss lady. The former is a pervert and seems to have some weird kinks. The latter stated that she likes to be on top, and she takes pleasure when the man is the bottom. Plus, she proposed the no violence rule which is kinda a flag(?) I think...?
Liar - Probably the most obvious one of them all, the girl who proposed the "no lying" rule.
The other 2 girls who willingly participated are:
The secretive chick = Seems like she's an undercover cop/a relative of any of the 3 dead men out for revenge, on the chase for the killer.
Either boss lady or the glasses girl = It could go either way for both of them really. Boss lady could be simply interested in the celeb, as she previously said; Glasses girl could simply be a pervert.
We'll see as this progress. Needless to say, looking forward to the upcoming chapters.