Slightly off the main point, if you are teaching 4 modules you are going to find yourself standing in front of the class for quite a lot of their timetable. You will need to very clearly define which class you are teaching at any particular time.
Give them a few minutes break between classes (about as much as would take them to move from one to another, about 5 minutes.) Then insist that work from the previous class is put away and define every time what subject you are doing now - write it on the board if necessary.
There is a tendency to think 'its Miss X (or Upsy) so it must be subject Y' and the notes go in the wrong book.
On the other hand, if there is a piece of work that would do just as well for two subjects, there is usually no reason why you cannot tell them to submit a copy of the same work into two folders. This is sometimes done between subjects with different teachers, and if it is appropriate you can have a theme running through a course so that this happens deliberately. Not so likely with your subjects, but it can be done.
Years ago, when I started as a substitute I was given a timetable, 8 classes, and left to get on with hauling them all through end of year between March and May. Training!!! I didn't even know what a module was! Now there are elaborate things called induction, mentoring and training... (it worked out ok