Call a house meeting and discuss the issue. Notes are passive aggressive and not effective. If you, as a couple, approach people individually you're going to make them feel outnumbered and back them into a corner. The only option is to sit everyone down as a group.
As a side note, I understand the situation as I myself was in it when I moved over initially. At the end of the day, even if they do clean it will never be to your own standards, and as soon as possible it's just best to get your own place.