Who is who?

I apologies straight off I'm an anglo male but all the girls look the same, I can't work out who is who.

- Who was the dead green person in the hospital, is it the mum?
- If she is (or even if she isn't) how did she die in the hospital?
- The older daughter, is she the one hurting everyone so they go to the hospital?
- The older daughter is Yumi, is that correct?
- In the lecture, the girl in front of them is spoken to, does she have anything to do with the movie after that?
- The mother that showed the daughter that her grandmother was dead, is that the same mother who walks in and sees that the older daughter cut the younger daughter?
- Why did the mother show the daughter that her grandmother was dead? (if the older daughter is the evil masochistic one, why did the mother do something so evil?)
- Who is actually killing everyone?
- Who is the little girl at the Yumi's front door?
- In the hospital at the end, in the room is it Yumi or the ghost changed into Yumi's body?