I have to say I have no experience of using Paypal for courses whatsoever as I work in a school where it's free! However our teachers regularly share courses with separate groups using the group enrolment key. Clicking on the name of the teacher in the course summary (which is only visible if you actually choose to have it there in site admin>appearance -we don't) will only show their profile - if you wanted the student to choose a teacher to enrol with you'd have to offer an enrolment key for each particular teacher - which you could do on that summary page I suppose. For example, the group enrolment keys for our students are the name of the classes they are in-which they see on their timetable, so they put themselves into the correct class. You could maybe give the key as the name of each of the 4 teachers -so if a student typed in Mr Smith as the enrolment key, he would get put automatically into Mr Smith's class and so on. Does that make sense?
Oh -also - it is well worth investigating groupings, which enable teachers to share a course yet only show their own materials to their own classes. I put something in the Moodle docs on this if you do a search on groupings. That might suit you too.